diff --git a/CMakeLists.txt b/CMakeLists.txt
index eaaa854c4f7e..8ccff3d1251e 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -186,6 +186,7 @@ set(SERVER_SOURCES
         ./src/chain.cpp
         ./src/checkpoints.cpp
         ./src/consensus/tx_verify.cpp
+        ./src/flatfile.cpp
         ./src/httprpc.cpp
         ./src/httpserver.cpp
         ./src/indirectmap.h
@@ -416,7 +417,7 @@ set(UTIL_SOURCES
         ./src/arith_uint256.cpp
         ./src/uint256.cpp
         ./src/util/threadnames.cpp
-        ./src/util.cpp
+        ./src/util/system.cpp
         ./src/utilstrencodings.cpp
         ./src/utilmoneystr.cpp
         ./src/utiltime.cpp
diff --git a/src/Makefile.am b/src/Makefile.am
index 75a59b125d0d..2517edf8cbb4 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -190,6 +190,7 @@ BITCOIN_CORE_H = \
   pairresult.h \
   addressbook.h \
   wallet/db.h \
+  flatfile.h \
   fs.h \
   hash.h \
   httprpc.h \
@@ -283,7 +284,7 @@ BITCOIN_CORE_H = \
   uint256.h \
   undo.h \
   util/memory.h \
-  util.h \
+  util/system.h \
   util/macros.h \
   util/threadnames.h \
   utilstrencodings.h \
@@ -326,6 +327,7 @@ libbitcoin_server_a_SOURCES = \
   checkpoints.cpp \
   consensus/params.cpp \
   consensus/tx_verify.cpp \
+  flatfile.cpp \
   consensus/zerocoin_verify.cpp \
   evo/deterministicmns.cpp \
   evo/evodb.cpp \
@@ -546,7 +548,7 @@ libbitcoin_util_a_SOURCES = \
   sync.cpp \
   threadinterrupt.cpp \
   uint256.cpp \
-  util.cpp \
+  util/system.cpp \
   utilmoneystr.cpp \
   util/threadnames.cpp \
   utilstrencodings.cpp \
diff --git a/src/Makefile.test.include b/src/Makefile.test.include
index 9c47b8287945..a3bf6225cdb6 100644
--- a/src/Makefile.test.include
+++ b/src/Makefile.test.include
@@ -64,6 +64,7 @@ BITCOIN_TESTS =\
   test/DoS_tests.cpp \
   test/evo_deterministicmns_tests.cpp \
   test/evo_specialtx_tests.cpp \
+  test/flatfile_tests.cpp \
   test/getarg_tests.cpp \
   test/hash_tests.cpp \
   test/key_tests.cpp \
diff --git a/src/addrdb.cpp b/src/addrdb.cpp
index cdd67f1f19a3..318bd7e96374 100644
--- a/src/addrdb.cpp
+++ b/src/addrdb.cpp
@@ -14,7 +14,7 @@
 #include "random.h"
 #include "streams.h"
 #include "tinyformat.h"
-#include "util.h"
+#include "util/system.h"
 
 namespace {
 
diff --git a/src/addrman.h b/src/addrman.h
index 872916686547..b78d391959aa 100644
--- a/src/addrman.h
+++ b/src/addrman.h
@@ -12,7 +12,7 @@
 #include "random.h"
 #include "sync.h"
 #include "timedata.h"
-#include "util.h"
+#include "util/system.h"
 
 #include <map>
 #include <set>
diff --git a/src/bench/bench_pivx.cpp b/src/bench/bench_pivx.cpp
index 9bf3993397cb..aa3ac218b479 100644
--- a/src/bench/bench_pivx.cpp
+++ b/src/bench/bench_pivx.cpp
@@ -6,7 +6,7 @@
 #include "bench.h"
 
 #include "key.h"
-#include "util.h"
+#include "util/system.h"
 
 int
 main(int argc, char** argv)
diff --git a/src/bench/checkqueue.cpp b/src/bench/checkqueue.cpp
index 5e1fa93fac5e..6a1bfacfdd01 100644
--- a/src/bench/checkqueue.cpp
+++ b/src/bench/checkqueue.cpp
@@ -3,7 +3,7 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include "bench.h"
-#include "util.h"
+#include "util/system.h"
 #include "checkqueue.h"
 #include "prevector.h"
 #include "random.h"
diff --git a/src/bip38.cpp b/src/bip38.cpp
index fa4516cf98c9..e83f81b1d09f 100644
--- a/src/bip38.cpp
+++ b/src/bip38.cpp
@@ -8,7 +8,7 @@
 #include "crypto/aes.h"
 #include "hash.h"
 #include "pubkey.h"
-#include "util.h"
+#include "util/system.h"
 #include "utilstrencodings.h"
 #include "random.h"
 
diff --git a/src/blockassembler.cpp b/src/blockassembler.cpp
index e500ffccc1ce..c86a6b5e440d 100644
--- a/src/blockassembler.cpp
+++ b/src/blockassembler.cpp
@@ -21,7 +21,7 @@
 #include "spork.h"
 #include "timedata.h"
 #include "txmempool.h"
-#include "util.h"
+#include "util/system.h"
 #include "validation.h"
 #include "validationinterface.h"
 
diff --git a/src/chain.cpp b/src/chain.cpp
index 5a14cacdf2b4..5691d31d59da 100644
--- a/src/chain.cpp
+++ b/src/chain.cpp
@@ -142,9 +142,9 @@ std::string CBlockIndex::ToString() const
         GetBlockHash().ToString());
 }
 
-CDiskBlockPos CBlockIndex::GetBlockPos() const
+FlatFilePos CBlockIndex::GetBlockPos() const
 {
-    CDiskBlockPos ret;
+    FlatFilePos ret;
     if (nStatus & BLOCK_HAVE_DATA) {
         ret.nFile = nFile;
         ret.nPos = nDataPos;
@@ -152,9 +152,9 @@ CDiskBlockPos CBlockIndex::GetBlockPos() const
     return ret;
 }
 
-CDiskBlockPos CBlockIndex::GetUndoPos() const
+FlatFilePos CBlockIndex::GetUndoPos() const
 {
-    CDiskBlockPos ret;
+    FlatFilePos ret;
     if (nStatus & BLOCK_HAVE_UNDO) {
         ret.nFile = nFile;
         ret.nPos = nUndoPos;
diff --git a/src/chain.h b/src/chain.h
index 6c80e254bdb0..fd16e8e5f68c 100644
--- a/src/chain.h
+++ b/src/chain.h
@@ -11,13 +11,14 @@
 #define BITCOIN_CHAIN_H
 
 #include "chainparams.h"
+#include "flatfile.h"
 #include "optional.h"
 #include "pow.h"
 #include "primitives/block.h"
 #include "timedata.h"
 #include "tinyformat.h"
 #include "uint256.h"
-#include "util.h"
+#include "util/system.h"
 #include "libzerocoin/Denominations.h"
 
 #include <vector>
@@ -87,47 +88,6 @@ class CBlockFileInfo
     }
 };
 
-struct CDiskBlockPos {
-    int nFile;
-    unsigned int nPos;
-
-    ADD_SERIALIZE_METHODS;
-
-    template <typename Stream, typename Operation>
-    inline void SerializationOp(Stream& s, Operation ser_action) {
-        READWRITE(VARINT(nFile, VarIntMode::NONNEGATIVE_SIGNED));
-        READWRITE(VARINT(nPos));
-    }
-
-    CDiskBlockPos()
-    {
-        SetNull();
-    }
-
-    CDiskBlockPos(int nFileIn, unsigned int nPosIn)
-    {
-        nFile = nFileIn;
-        nPos = nPosIn;
-    }
-
-    friend bool operator==(const CDiskBlockPos& a, const CDiskBlockPos& b)
-    {
-        return (a.nFile == b.nFile && a.nPos == b.nPos);
-    }
-
-    friend bool operator!=(const CDiskBlockPos& a, const CDiskBlockPos& b)
-    {
-        return !(a == b);
-    }
-
-    void SetNull()
-    {
-        nFile = -1;
-        nPos = 0;
-    }
-    bool IsNull() const { return (nFile == -1); }
-};
-
 enum BlockStatus {
     //! Unused.
     BLOCK_VALID_UNKNOWN = 0,
@@ -253,8 +213,8 @@ class CBlockIndex
 
     std::string ToString() const;
 
-    CDiskBlockPos GetBlockPos() const;
-    CDiskBlockPos GetUndoPos() const;
+    FlatFilePos GetBlockPos() const;
+    FlatFilePos GetUndoPos() const;
     CBlockHeader GetBlockHeader() const;
     uint256 GetBlockHash() const { return *phashBlock; }
     int64_t GetBlockTime() const { return (int64_t)nTime; }
diff --git a/src/chainparamsbase.cpp b/src/chainparamsbase.cpp
index 3b5b98b3dab8..849a850c8587 100644
--- a/src/chainparamsbase.cpp
+++ b/src/chainparamsbase.cpp
@@ -7,7 +7,7 @@
 #include "chainparamsbase.h"
 
 #include "tinyformat.h"
-#include "util.h"
+#include "util/system.h"
 
 #include <assert.h>
 
diff --git a/src/consensus/params.cpp b/src/consensus/params.cpp
index b0fdae284755..ef28d107065c 100644
--- a/src/consensus/params.cpp
+++ b/src/consensus/params.cpp
@@ -5,7 +5,7 @@
 
 #include "consensus/params.h"
 #include "consensus/upgrades.h"
-#include "util.h"
+#include "util/system.h"
 
 namespace Consensus {
 
diff --git a/src/core_read.cpp b/src/core_read.cpp
index b9a6eef164d0..9509b4015075 100644
--- a/src/core_read.cpp
+++ b/src/core_read.cpp
@@ -10,7 +10,7 @@
 #include "script/script.h"
 #include "serialize.h"
 #include "streams.h"
-#include "util.h"
+#include "util/system.h"
 #include "utilstrencodings.h"
 #include "version.h"
 
diff --git a/src/core_write.cpp b/src/core_write.cpp
index 266e95e0deeb..041fcc5563cf 100644
--- a/src/core_write.cpp
+++ b/src/core_write.cpp
@@ -13,7 +13,7 @@
 #include "serialize.h"
 #include "streams.h"
 #include <univalue.h>
-#include "util.h"
+#include "util/system.h"
 #include "utilmoneystr.h"
 #include "utilstrencodings.h"
 
diff --git a/src/crypter.cpp b/src/crypter.cpp
index f0929f74fb53..83420a3c0486 100644
--- a/src/crypter.cpp
+++ b/src/crypter.cpp
@@ -9,7 +9,7 @@
 #include "crypto/sha512.h"
 #include "script/script.h"
 #include "script/standard.h"
-#include "util.h"
+#include "util/system.h"
 #include "init.h"
 #include "uint256.h"
 
diff --git a/src/dbwrapper.cpp b/src/dbwrapper.cpp
index 5ac82fb2dc5f..f44b613cf497 100644
--- a/src/dbwrapper.cpp
+++ b/src/dbwrapper.cpp
@@ -4,7 +4,7 @@
 
 #include "dbwrapper.h"
 
-#include "util.h"
+#include "util/system.h"
 
 #include <leveldb/cache.h>
 #include <leveldb/env.h>
diff --git a/src/dbwrapper.h b/src/dbwrapper.h
index 3889651a9d71..dd0a48c24b28 100644
--- a/src/dbwrapper.h
+++ b/src/dbwrapper.h
@@ -9,7 +9,7 @@
 #include "fs.h"
 #include "serialize.h"
 #include "streams.h"
-#include "util.h"
+#include "util/system.h"
 #include "version.h"
 
 #include <typeindex>
diff --git a/src/flatfile.cpp b/src/flatfile.cpp
new file mode 100644
index 000000000000..ec136272e7c3
--- /dev/null
+++ b/src/flatfile.cpp
@@ -0,0 +1,98 @@
+// Copyright (c) 2009-2010 Satoshi Nakamoto
+// Copyright (c) 2009-2019 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <stdexcept>
+
+#include "flatfile.h"
+#include "logging.h"
+#include "tinyformat.h"
+#include "util/system.h"
+
+FlatFileSeq::FlatFileSeq(fs::path dir, const char* prefix, size_t chunk_size) :
+    m_dir(std::move(dir)),
+    m_prefix(prefix),
+    m_chunk_size(chunk_size)
+{
+    if (chunk_size == 0) {
+        throw std::invalid_argument("chunk_size must be positive");
+    }
+}
+
+std::string FlatFilePos::ToString() const
+{
+    return strprintf("FlatFilePos(nFile=%i, nPos=%i)", nFile, nPos);
+}
+
+fs::path FlatFileSeq::FileName(const FlatFilePos& pos) const
+{
+    return m_dir / strprintf("%s%05u.dat", m_prefix, pos.nFile);
+}
+
+FILE* FlatFileSeq::Open(const FlatFilePos& pos, bool read_only)
+{
+    if (pos.IsNull()) {
+        return nullptr;
+    }
+    fs::path path = FileName(pos);
+    fs::create_directories(path.parent_path());
+    FILE* file = fsbridge::fopen(path, read_only ? "rb": "rb+");
+    if (!file && !read_only)
+        file = fsbridge::fopen(path, "wb+");
+    if (!file) {
+        LogPrintf("Unable to open file %s\n", path.string());
+        return nullptr;
+    }
+    if (pos.nPos && fseek(file, pos.nPos, SEEK_SET)) {
+        LogPrintf("Unable to seek to position %u of %s\n", pos.nPos, path.string());
+        fclose(file);
+        return nullptr;
+    }
+    return file;
+}
+
+size_t FlatFileSeq::Allocate(const FlatFilePos& pos, size_t add_size, bool& out_of_space)
+{
+    out_of_space = false;
+
+    unsigned int n_old_chunks = (pos.nPos + m_chunk_size - 1) / m_chunk_size;
+    unsigned int n_new_chunks = (pos.nPos + add_size + m_chunk_size - 1) / m_chunk_size;
+    if (n_new_chunks > n_old_chunks) {
+        size_t old_size = pos.nPos;
+        size_t new_size = n_new_chunks * m_chunk_size;
+        size_t inc_size = new_size - old_size;
+
+        if (CheckDiskSpace(m_dir, inc_size)) {
+            FILE *file = Open(pos);
+            if (file) {
+                LogPrintf("Pre-allocating up to position 0x%x in %s%05u.dat\n", new_size, m_prefix, pos.nFile);
+                AllocateFileRange(file, pos.nPos, inc_size);
+                fclose(file);
+                return inc_size;
+            }
+        } else {
+            out_of_space = true;
+        }
+    }
+    return 0;
+}
+
+bool FlatFileSeq::Flush(const FlatFilePos& pos, bool finalize)
+{
+    FILE* file = Open(FlatFilePos(pos.nFile, 0)); // Avoid fseek to nPos
+    if (!file) {
+        return error("%s: failed to open file %d", __func__, pos.nFile);
+    }
+    if (finalize && !TruncateFile(file, pos.nPos)) {
+        fclose(file);
+        return error("%s: failed to truncate file %d", __func__, pos.nFile);
+    }
+    if (!FileCommit(file)) {
+        fclose(file);
+        return error("%s: failed to commit file %d", __func__, pos.nFile);
+    }
+
+    fclose(file);
+    return true;
+}
diff --git a/src/flatfile.h b/src/flatfile.h
new file mode 100644
index 000000000000..17eaaeb7b09d
--- /dev/null
+++ b/src/flatfile.h
@@ -0,0 +1,96 @@
+// Copyright (c) 2009-2010 Satoshi Nakamoto
+// Copyright (c) 2009-2019 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#ifndef BITCOIN_FLATFILE_H
+#define BITCOIN_FLATFILE_H
+
+#include <string>
+
+#include "fs.h"
+#include "serialize.h"
+
+struct FlatFilePos
+{
+    int nFile;
+    unsigned int nPos;
+
+    ADD_SERIALIZE_METHODS;
+
+    template <typename Stream, typename Operation>
+    inline void SerializationOp(Stream& s, Operation ser_action) {
+        READWRITE(VARINT(nFile, VarIntMode::NONNEGATIVE_SIGNED));
+        READWRITE(VARINT(nPos));
+    }
+
+    FlatFilePos() : nFile(-1), nPos(0) {}
+
+    FlatFilePos(int nFileIn, unsigned int nPosIn) :
+        nFile(nFileIn),
+        nPos(nPosIn)
+    {}
+
+    friend bool operator==(const FlatFilePos &a, const FlatFilePos &b) {
+        return (a.nFile == b.nFile && a.nPos == b.nPos);
+    }
+
+    friend bool operator!=(const FlatFilePos &a, const FlatFilePos &b) {
+        return !(a == b);
+    }
+
+    void SetNull() { nFile = -1; nPos = 0; }
+    bool IsNull() const { return (nFile == -1); }
+
+    std::string ToString() const;
+};
+
+/**
+ * FlatFileSeq represents a sequence of numbered files storing raw data. This class facilitates
+ * access to and efficient management of these files.
+ */
+class FlatFileSeq
+{
+private:
+    const fs::path m_dir;
+    const char* const m_prefix;
+    const size_t m_chunk_size;
+
+public:
+    /**
+     * Constructor
+     *
+     * @param dir The base directory that all files live in.
+     * @param prefix A short prefix given to all file names.
+     * @param chunk_size Disk space is pre-allocated in multiples of this amount.
+     */
+    FlatFileSeq(fs::path dir, const char* prefix, size_t chunk_size);
+
+    /** Get the name of the file at the given position. */
+    fs::path FileName(const FlatFilePos& pos) const;
+
+    /** Open a handle to the file at the given position. */
+    FILE* Open(const FlatFilePos& pos, bool read_only = false);
+
+    /**
+     * Allocate additional space in a file after the given starting position. The amount allocated
+     * will be the minimum multiple of the sequence chunk size greater than add_size.
+     *
+     * @param[in] pos The starting position that bytes will be allocated after.
+     * @param[in] add_size The minimum number of bytes to be allocated.
+     * @param[out] out_of_space Whether the allocation failed due to insufficient disk space.
+     * @return The number of bytes successfully allocated.
+     */
+    size_t Allocate(const FlatFilePos& pos, size_t add_size, bool& out_of_space);
+
+    /**
+     * Commit a file to disk, and optionally truncate off extra pre-allocated bytes if final.
+     *
+     * @param[in] pos The first unwritten position in the file to be flushed.
+     * @param[in] finalize True if no more data will be written to this file.
+     * @return true on success, false on failure.
+     */
+    bool Flush(const FlatFilePos& pos, bool finalize = false);
+};
+
+#endif // BITCOIN_FLATFILE_H
diff --git a/src/httprpc.cpp b/src/httprpc.cpp
index 56bf3047c8b4..24db0d455414 100644
--- a/src/httprpc.cpp
+++ b/src/httprpc.cpp
@@ -13,7 +13,7 @@
 #include "rpc/server.h"
 #include "random.h"
 #include "sync.h"
-#include "util.h"
+#include "util/system.h"
 #include "utilstrencodings.h"
 #include "guiinterface.h"
 
diff --git a/src/httpserver.cpp b/src/httpserver.cpp
index 02317dbea12c..ed88665cfe93 100644
--- a/src/httpserver.cpp
+++ b/src/httpserver.cpp
@@ -7,7 +7,7 @@
 
 #include "chainparamsbase.h"
 #include "compat.h"
-#include "util.h"
+#include "util/system.h"
 #include "netbase.h"
 #include "rpc/protocol.h" // For HTTP status codes
 #include "sync.h"
diff --git a/src/init.cpp b/src/init.cpp
index 200d6ea340dc..002ff1f954b3 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -50,7 +50,7 @@
 #include "torcontrol.h"
 #include "guiinterface.h"
 #include "guiinterfaceutil.h"
-#include "util.h"
+#include "util/system.h"
 #include "utilmoneystr.h"
 #include "util/threadnames.h"
 #include "validation.h"
@@ -688,8 +688,8 @@ void ThreadImport(const std::vector<fs::path>& vImportFiles)
         CImportingNow imp;
         int nFile = 0;
         while (true) {
-            CDiskBlockPos pos(nFile, 0);
-            if (!fs::exists(GetBlockPosFilename(pos, "blk")))
+            FlatFilePos pos(nFile, 0);
+            if (!fs::exists(GetBlockPosFilename(pos)))
                 break; // No block files left to reindex
             FILE* file = OpenBlockFile(pos, true);
             if (!file)
@@ -1735,11 +1735,11 @@ bool AppInitMain()
 #endif
     // ********************************************************* Step 9: import blocks
 
-    if (!CheckDiskSpace(/* additional_bytes */ 0, /* blocks_dir */ false)) {
+    if (!CheckDiskSpace(GetDataDir())) {
         UIError(strprintf(_("Error: Disk space is low for %s"), GetDataDir()));
         return false;
     }
-    if (!CheckDiskSpace(/* additional_bytes */ 0, /* blocks_dir */ true)) {
+    if (!CheckDiskSpace(GetBlocksDir())) {
         UIError(strprintf(_("Error: Disk space is low for %s"), GetBlocksDir()));
         return false;
     }
diff --git a/src/kernel.cpp b/src/kernel.cpp
index 0b41f9755ab9..a764bef3af31 100644
--- a/src/kernel.cpp
+++ b/src/kernel.cpp
@@ -12,7 +12,7 @@
 #include "policy/policy.h"
 #include "script/interpreter.h"
 #include "stakeinput.h"
-#include "util.h"
+#include "util/system.h"
 #include "utilmoneystr.h"
 #include "validation.h"
 #include "zpivchain.h"
diff --git a/src/keystore.cpp b/src/keystore.cpp
index 47e8fa5723b2..09c3390b17c6 100644
--- a/src/keystore.cpp
+++ b/src/keystore.cpp
@@ -10,7 +10,7 @@
 #include "key.h"
 #include "script/script.h"
 #include "script/standard.h"
-#include "util.h"
+#include "util/system.h"
 
 
 bool CKeyStore::AddKey(const CKey& key)
diff --git a/src/libzerocoin/Coin.h b/src/libzerocoin/Coin.h
index 290acc12af5f..8860d41c48d6 100644
--- a/src/libzerocoin/Coin.h
+++ b/src/libzerocoin/Coin.h
@@ -17,7 +17,7 @@
 #include "Params.h"
 #include "amount.h"
 #include "bignum.h"
-#include "util.h"
+#include "util/system.h"
 #include "key.h"
 
 namespace libzerocoin
diff --git a/src/masternode-payments.cpp b/src/masternode-payments.cpp
index b06d8fb741b7..9ae558cfa265 100644
--- a/src/masternode-payments.cpp
+++ b/src/masternode-payments.cpp
@@ -15,7 +15,7 @@
 #include "net_processing.h"
 #include "spork.h"
 #include "sync.h"
-#include "util.h"
+#include "util/system.h"
 #include "utilmoneystr.h"
 
 
diff --git a/src/masternode-sync.cpp b/src/masternode-sync.cpp
index a7352ebaf803..7fcec9276c9b 100644
--- a/src/masternode-sync.cpp
+++ b/src/masternode-sync.cpp
@@ -12,7 +12,7 @@
 #include "masternodeman.h"
 #include "netmessagemaker.h"
 #include "spork.h"
-#include "util.h"
+#include "util/system.h"
 #include "addrman.h"
 // clang-format on
 
diff --git a/src/masternode.cpp b/src/masternode.cpp
index 2e566b56c9f8..a4780d0635c1 100644
--- a/src/masternode.cpp
+++ b/src/masternode.cpp
@@ -11,7 +11,7 @@
 #include "masternodeman.h"
 #include "netbase.h"
 #include "sync.h"
-#include "util.h"
+#include "util/system.h"
 #include "wallet/wallet.h"
 
 #define MASTERNODE_MIN_CONFIRMATIONS_REGTEST 1
diff --git a/src/masternode.h b/src/masternode.h
index 20f0bd1ab9bd..048826fb393a 100644
--- a/src/masternode.h
+++ b/src/masternode.h
@@ -13,7 +13,7 @@
 #include "serialize.h"
 #include "sync.h"
 #include "timedata.h"
-#include "util.h"
+#include "util/system.h"
 
 /* Depth of the block pinged by masternodes */
 static const unsigned int MNPING_DEPTH = 12;
diff --git a/src/masternodeconfig.cpp b/src/masternodeconfig.cpp
index 265e4b91a521..8e156b21a512 100644
--- a/src/masternodeconfig.cpp
+++ b/src/masternodeconfig.cpp
@@ -6,7 +6,7 @@
 
 #include "fs.h"
 #include "netbase.h"
-#include "util.h"
+#include "util/system.h"
 #include "guiinterface.h"
 #include <base58.h>
 
diff --git a/src/masternodeman.cpp b/src/masternodeman.cpp
index c4e52e57e584..fd38d3e3873a 100644
--- a/src/masternodeman.cpp
+++ b/src/masternodeman.cpp
@@ -16,7 +16,7 @@
 #include "netmessagemaker.h"
 #include "net_processing.h"
 #include "spork.h"
-#include "util.h"
+#include "util/system.h"
 
 #include <boost/thread/thread.hpp>
 
diff --git a/src/masternodeman.h b/src/masternodeman.h
index e675ad0f6684..1859304df0ee 100644
--- a/src/masternodeman.h
+++ b/src/masternodeman.h
@@ -13,7 +13,7 @@
 #include "masternode.h"
 #include "net.h"
 #include "sync.h"
-#include "util.h"
+#include "util/system.h"
 
 #define MASTERNODES_DUMP_SECONDS (15 * 60)
 #define MASTERNODES_DSEG_SECONDS (3 * 60 * 60)
diff --git a/src/messagesigner.cpp b/src/messagesigner.cpp
index 386f47c86885..46df3e55b824 100644
--- a/src/messagesigner.cpp
+++ b/src/messagesigner.cpp
@@ -7,7 +7,7 @@
 #include "hash.h"
 #include "messagesigner.h"
 #include "tinyformat.h"
-#include "util.h"
+#include "util/system.h"
 #include "utilstrencodings.h"
 
 const std::string strMessageMagic = "DarkNet Signed Message:\n";
diff --git a/src/miner.cpp b/src/miner.cpp
index 68291fc60ef2..8aa545d9b1ea 100644
--- a/src/miner.cpp
+++ b/src/miner.cpp
@@ -20,7 +20,7 @@
 #include "primitives/block.h"
 #include "primitives/transaction.h"
 #include "timedata.h"
-#include "util.h"
+#include "util/system.h"
 #include "utilmoneystr.h"
 #ifdef ENABLE_WALLET
 #include "wallet/wallet.h"
diff --git a/src/netbase.cpp b/src/netbase.cpp
index 442260e58a81..12123fd47f13 100644
--- a/src/netbase.cpp
+++ b/src/netbase.cpp
@@ -14,7 +14,7 @@
 #include "sync.h"
 #include "uint256.h"
 #include "random.h"
-#include "util.h"
+#include "util/system.h"
 #include "utilstrencodings.h"
 
 #include <atomic>
diff --git a/src/noui.cpp b/src/noui.cpp
index 147d61cdb81e..20b280ae8ecf 100644
--- a/src/noui.cpp
+++ b/src/noui.cpp
@@ -8,7 +8,7 @@
 #include "noui.h"
 
 #include "guiinterface.h"
-#include "util.h"
+#include "util/system.h"
 
 #include <cstdio>
 #include <stdint.h>
diff --git a/src/pivx-cli.cpp b/src/pivx-cli.cpp
index f98fcb1f619b..9775106c6d2e 100644
--- a/src/pivx-cli.cpp
+++ b/src/pivx-cli.cpp
@@ -10,7 +10,7 @@
 #include "fs.h"
 #include "rpc/client.h"
 #include "rpc/protocol.h"
-#include "util.h"
+#include "util/system.h"
 #include "utilstrencodings.h"
 
 #include <stdio.h>
diff --git a/src/pivx-tx.cpp b/src/pivx-tx.cpp
index 94259d7bfdc8..1621aff68ecf 100644
--- a/src/pivx-tx.cpp
+++ b/src/pivx-tx.cpp
@@ -14,7 +14,7 @@
 #include "script/script.h"
 #include "script/sign.h"
 #include <univalue.h>
-#include "util.h"
+#include "util/system.h"
 #include "utilmoneystr.h"
 #include "utilstrencodings.h"
 
diff --git a/src/pivxd.cpp b/src/pivxd.cpp
index bcde06ae07e0..ad02677ccc8f 100644
--- a/src/pivxd.cpp
+++ b/src/pivxd.cpp
@@ -12,7 +12,7 @@
 #include "masternodeconfig.h"
 #include "noui.h"
 #include "rpc/server.h"
-#include "util.h"
+#include "util/system.h"
 
 #include <stdio.h>
 
diff --git a/src/policy/fees.cpp b/src/policy/fees.cpp
index 93f789175260..3e2c169c99c9 100644
--- a/src/policy/fees.cpp
+++ b/src/policy/fees.cpp
@@ -10,7 +10,7 @@
 #include "primitives/transaction.h"
 #include "streams.h"
 #include "txmempool.h"
-#include "util.h"
+#include "util/system.h"
 
 void TxConfirmStats::Initialize(std::vector<double>& defaultBuckets,
                                 unsigned int maxConfirms, double _decay)
diff --git a/src/policy/policy.cpp b/src/policy/policy.cpp
index 41f61031449b..deae2082bead 100644
--- a/src/policy/policy.cpp
+++ b/src/policy/policy.cpp
@@ -9,7 +9,7 @@
 
 #include "consensus/tx_verify.h" // for IsFinal()
 #include "tinyformat.h"
-#include "util.h"
+#include "util/system.h"
 #include "utilstrencodings.h"
 #include "validation.h"
 
diff --git a/src/pow.cpp b/src/pow.cpp
index 384cb742957c..6b41d9796956 100644
--- a/src/pow.cpp
+++ b/src/pow.cpp
@@ -11,7 +11,7 @@
 #include "chainparams.h"
 #include "primitives/block.h"
 #include "uint256.h"
-#include "util.h"
+#include "util/system.h"
 
 #include <math.h>
 
diff --git a/src/primitives/block.cpp b/src/primitives/block.cpp
index 84c32be40eae..e0b7fd2d618c 100644
--- a/src/primitives/block.cpp
+++ b/src/primitives/block.cpp
@@ -11,7 +11,7 @@
 #include "script/sign.h"
 #include "tinyformat.h"
 #include "utilstrencodings.h"
-#include "util.h"
+#include "util/system.h"
 
 uint256 CBlockHeader::GetHash() const
 {
diff --git a/src/protocol.cpp b/src/protocol.cpp
index ea570180ff1b..f40fc79aed7e 100644
--- a/src/protocol.cpp
+++ b/src/protocol.cpp
@@ -7,7 +7,7 @@
 
 #include "protocol.h"
 
-#include "util.h"
+#include "util/system.h"
 #include "utilstrencodings.h"
 
 #ifndef WIN32
diff --git a/src/qt/clientmodel.cpp b/src/qt/clientmodel.cpp
index 136faffd829e..51096dcabaa4 100644
--- a/src/qt/clientmodel.cpp
+++ b/src/qt/clientmodel.cpp
@@ -19,7 +19,7 @@
 #include "net.h"
 #include "netbase.h"
 #include "guiinterface.h"
-#include "util.h"
+#include "util/system.h"
 #include "warnings.h"
 
 #include <stdint.h>
diff --git a/src/qt/guiutil.cpp b/src/qt/guiutil.cpp
index c13d07b808c0..ba4a73b4336a 100644
--- a/src/qt/guiutil.cpp
+++ b/src/qt/guiutil.cpp
@@ -17,7 +17,7 @@
 #include "protocol.h"
 #include "script/script.h"
 #include "script/standard.h"
-#include "util.h"
+#include "util/system.h"
 
 #ifdef WIN32
 #ifdef _WIN32_WINNT
diff --git a/src/qt/intro.cpp b/src/qt/intro.cpp
index 1ed9cf798598..28f8a1e99fde 100644
--- a/src/qt/intro.cpp
+++ b/src/qt/intro.cpp
@@ -10,7 +10,7 @@
 #include "fs.h"
 #include "guiutil.h"
 
-#include "util.h"
+#include "util/system.h"
 #include "qt/pivx/qtutils.h"
 
 #include <QFileDialog>
diff --git a/src/qt/optionsmodel.cpp b/src/qt/optionsmodel.cpp
index 09c1a585bd80..7f4d39da2702 100644
--- a/src/qt/optionsmodel.cpp
+++ b/src/qt/optionsmodel.cpp
@@ -18,7 +18,7 @@
 #include "net.h"
 #include "netbase.h"
 #include "txdb.h" // for -dbcache defaults
-#include "util.h"
+#include "util/system.h"
 
 #ifdef ENABLE_WALLET
 #include "masternodeconfig.h"
diff --git a/src/qt/paymentserver.cpp b/src/qt/paymentserver.cpp
index f8265c4fd027..a9554e7c5b30 100644
--- a/src/qt/paymentserver.cpp
+++ b/src/qt/paymentserver.cpp
@@ -14,7 +14,7 @@
 #include "base58.h"
 #include "chainparams.h"
 #include "guiinterface.h"
-#include "util.h"
+#include "util/system.h"
 #include "wallet/wallet.h"
 
 #include <cstdlib>
diff --git a/src/qt/pivx.cpp b/src/qt/pivx.cpp
index d0b9a4d76c68..b96eddba4208 100644
--- a/src/qt/pivx.cpp
+++ b/src/qt/pivx.cpp
@@ -33,7 +33,7 @@
 #include "init.h"
 #include "rpc/server.h"
 #include "guiinterface.h"
-#include "util.h"
+#include "util/system.h"
 #include "warnings.h"
 
 #ifdef ENABLE_WALLET
diff --git a/src/qt/pivx/masternodeswidget.cpp b/src/qt/pivx/masternodeswidget.cpp
index 722ade7abd02..f9b32472259c 100644
--- a/src/qt/pivx/masternodeswidget.cpp
+++ b/src/qt/pivx/masternodeswidget.cpp
@@ -21,7 +21,7 @@
 #include "sync.h"
 #include "wallet/wallet.h"
 #include "askpassphrasedialog.h"
-#include "util.h"
+#include "util/system.h"
 #include "qt/pivx/optionbutton.h"
 #include <iostream>
 #include <fstream>
diff --git a/src/qt/pivx/pivxgui.cpp b/src/qt/pivx/pivxgui.cpp
index 77594265f991..dadf137304d8 100644
--- a/src/qt/pivx/pivxgui.cpp
+++ b/src/qt/pivx/pivxgui.cpp
@@ -19,7 +19,7 @@
 #include "qt/pivx/defaultdialog.h"
 
 #include "init.h"
-#include "util.h"
+#include "util/system.h"
 
 #include <QApplication>
 #include <QColor>
diff --git a/src/qt/pivx/settings/settingsconsolewidget.cpp b/src/qt/pivx/settings/settingsconsolewidget.cpp
index 0e1fd165a542..2f991f004171 100644
--- a/src/qt/pivx/settings/settingsconsolewidget.cpp
+++ b/src/qt/pivx/settings/settingsconsolewidget.cpp
@@ -13,7 +13,7 @@
 
 #include "chainparams.h"
 #include "sapling/key_io_sapling.h"
-#include "util.h"
+#include "util/system.h"
 #include "utilitydialog.h"
 
 #ifdef ENABLE_WALLET
diff --git a/src/qt/pivx/settings/settingsinformationwidget.cpp b/src/qt/pivx/settings/settingsinformationwidget.cpp
index 2294a3ddbf0d..39fbf03ad7b1 100644
--- a/src/qt/pivx/settings/settingsinformationwidget.cpp
+++ b/src/qt/pivx/settings/settingsinformationwidget.cpp
@@ -8,7 +8,7 @@
 #include "clientmodel.h"
 #include "chainparams.h"
 #include "db.h"
-#include "util.h"
+#include "util/system.h"
 #include "guiutil.h"
 #include "qt/pivx/qtutils.h"
 
diff --git a/src/qt/pivx/splash.cpp b/src/qt/pivx/splash.cpp
index 149f72ff4fee..fa07fe393117 100644
--- a/src/qt/pivx/splash.cpp
+++ b/src/qt/pivx/splash.cpp
@@ -10,7 +10,7 @@
 #include "init.h"
 #include "guiinterface.h"
 #include "networkstyle.h"
-#include "util.h"
+#include "util/system.h"
 #include "version.h"
 #include "guiutil.h"
 
diff --git a/src/qt/rpcconsole.cpp b/src/qt/rpcconsole.cpp
index ac64e526d96b..10da3b125dc4 100644
--- a/src/qt/rpcconsole.cpp
+++ b/src/qt/rpcconsole.cpp
@@ -15,7 +15,7 @@
 
 #include "chainparams.h"
 #include "netbase.h"
-#include "util.h"
+#include "util/system.h"
 #ifdef ENABLE_WALLET
 #include "wallet/wallet.h"
 #endif // ENABLE_WALLET
diff --git a/src/qt/test/test_main.cpp b/src/qt/test/test_main.cpp
index 5a23c4e9a394..085aac9aff33 100644
--- a/src/qt/test/test_main.cpp
+++ b/src/qt/test/test_main.cpp
@@ -8,7 +8,7 @@
 #include "config/pivx-config.h"
 #endif
 
-#include "util.h"
+#include "util/system.h"
 #include "uritests.h"
 
 #include <QCoreApplication>
diff --git a/src/qt/transactiontablemodel.cpp b/src/qt/transactiontablemodel.cpp
index da2aaa375ede..1cea8e4f236e 100644
--- a/src/qt/transactiontablemodel.cpp
+++ b/src/qt/transactiontablemodel.cpp
@@ -16,7 +16,7 @@
 #include "interfaces/handler.h"
 #include "sync.h"
 #include "uint256.h"
-#include "util.h"
+#include "util/system.h"
 #include "wallet/wallet.h"
 
 #include <algorithm>
diff --git a/src/qt/utilitydialog.cpp b/src/qt/utilitydialog.cpp
index 089a58e5c8ea..6eea16dd421b 100644
--- a/src/qt/utilitydialog.cpp
+++ b/src/qt/utilitydialog.cpp
@@ -15,7 +15,7 @@
 #include "intro.h"
 #include "guiutil.h"
 #include "qt/pivx/qtutils.h"
-#include "util.h"
+#include "util/system.h"
 
 #include <stdio.h>
 
diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
index 395cbc6e79ec..a3d8d975e68a 100644
--- a/src/rpc/blockchain.cpp
+++ b/src/rpc/blockchain.cpp
@@ -18,7 +18,7 @@
 #include "rpc/server.h"
 #include "sync.h"
 #include "txdb.h"
-#include "util.h"
+#include "util/system.h"
 #include "utilmoneystr.h"
 #include "utilstrencodings.h"
 #include "hash.h"
diff --git a/src/rpc/misc.cpp b/src/rpc/misc.cpp
index 794b7fb4fd63..7ae80a8d0235 100644
--- a/src/rpc/misc.cpp
+++ b/src/rpc/misc.cpp
@@ -16,7 +16,7 @@
 #include "rpc/server.h"
 #include "spork.h"
 #include "timedata.h"
-#include "util.h"
+#include "util/system.h"
 #ifdef ENABLE_WALLET
 #include "wallet/wallet.h"
 #include "wallet/walletdb.h"
diff --git a/src/rpc/net.cpp b/src/rpc/net.cpp
index 110fae714870..66fc589ac83f 100644
--- a/src/rpc/net.cpp
+++ b/src/rpc/net.cpp
@@ -14,7 +14,7 @@
 #include "sync.h"
 #include "timedata.h"
 #include "guiinterface.h"
-#include "util.h"
+#include "util/system.h"
 #include "version.h"
 #include "validation.h"
 
diff --git a/src/rpc/protocol.cpp b/src/rpc/protocol.cpp
index 6e4fe2ca930c..a493397768e6 100644
--- a/src/rpc/protocol.cpp
+++ b/src/rpc/protocol.cpp
@@ -9,7 +9,7 @@
 
 #include "random.h"
 #include "tinyformat.h"
-#include "util.h"
+#include "util/system.h"
 #include "utilstrencodings.h"
 #include "utiltime.h"
 #include "version.h"
diff --git a/src/rpc/server.cpp b/src/rpc/server.cpp
index 482b317d8b32..7031123e07f3 100644
--- a/src/rpc/server.cpp
+++ b/src/rpc/server.cpp
@@ -13,7 +13,7 @@
 #include "random.h"
 #include "sync.h"
 #include "guiinterface.h"
-#include "util.h"
+#include "util/system.h"
 #include "utilstrencodings.h"
 
 #ifdef ENABLE_WALLET
diff --git a/src/sapling/crypter_sapling.cpp b/src/sapling/crypter_sapling.cpp
index 2921ca1d99c7..5860a4e89be4 100644
--- a/src/sapling/crypter_sapling.cpp
+++ b/src/sapling/crypter_sapling.cpp
@@ -7,7 +7,7 @@
 
 #include "script/script.h"
 #include "script/standard.h"
-#include "util.h"
+#include "util/system.h"
 #include "uint256.h"
 
 #include "wallet/wallet.h"
diff --git a/src/sapling/sapling_validation.cpp b/src/sapling/sapling_validation.cpp
index e2ac6f248c99..838ad45d400f 100644
--- a/src/sapling/sapling_validation.cpp
+++ b/src/sapling/sapling_validation.cpp
@@ -8,7 +8,7 @@
 #include "consensus/consensus.h" // for MAX_BLOCK_SIZE_CURRENT
 #include "script/interpreter.h" // for SigHash
 #include "consensus/validation.h" // for CValidationState
-#include "util.h" // for error()
+#include "util/system.h" // for error()
 #include "consensus/upgrades.h" // for CurrentEpochBranchId()
 
 #include <librustzcash.h>
diff --git a/src/script/ismine.cpp b/src/script/ismine.cpp
index e9312b4cf5e4..7394e7879a0c 100644
--- a/src/script/ismine.cpp
+++ b/src/script/ismine.cpp
@@ -11,7 +11,7 @@
 #include "script/script.h"
 #include "script/sign.h"
 #include "script/standard.h"
-#include "util.h"
+#include "util/system.h"
 
 
 
diff --git a/src/script/sigcache.cpp b/src/script/sigcache.cpp
index 37e0998da63c..c5198131354e 100644
--- a/src/script/sigcache.cpp
+++ b/src/script/sigcache.cpp
@@ -11,7 +11,7 @@
 #include "pubkey.h"
 #include "random.h"
 #include "uint256.h"
-#include "util.h"
+#include "util/system.h"
 
 #include <boost/thread/thread.hpp>
 
diff --git a/src/script/sign.cpp b/src/script/sign.cpp
index 7a34a872207b..12878f4fb885 100644
--- a/src/script/sign.cpp
+++ b/src/script/sign.cpp
@@ -12,7 +12,7 @@
 #include "primitives/transaction.h"
 #include "script/standard.h"
 #include "uint256.h"
-#include "util.h"
+#include "util/system.h"
 
 typedef std::vector<unsigned char> valtype;
 
diff --git a/src/spork.h b/src/spork.h
index 89d18955e3f6..814261e6daa2 100644
--- a/src/spork.h
+++ b/src/spork.h
@@ -13,7 +13,7 @@
 #include "net.h"
 #include "sporkid.h"
 #include "sync.h"
-#include "util.h"
+#include "util/system.h"
 
 #include "protocol.h"
 
diff --git a/src/test/CMakeLists.txt b/src/test/CMakeLists.txt
index 7d6403774ccd..db5df51ce43f 100644
--- a/src/test/CMakeLists.txt
+++ b/src/test/CMakeLists.txt
@@ -96,6 +96,7 @@ set(BITCOIN_TESTS
         ${CMAKE_CURRENT_SOURCE_DIR}/DoS_tests.cpp
         ${CMAKE_CURRENT_SOURCE_DIR}/evo_deterministicmns_tests.cpp
         ${CMAKE_CURRENT_SOURCE_DIR}/evo_specialtx_tests.cpp
+        ${CMAKE_CURRENT_SOURCE_DIR}/flatfile_tests.cpp
         ${CMAKE_CURRENT_SOURCE_DIR}/getarg_tests.cpp
         ${CMAKE_CURRENT_SOURCE_DIR}/hash_tests.cpp
         ${CMAKE_CURRENT_SOURCE_DIR}/key_tests.cpp
diff --git a/src/test/DoS_tests.cpp b/src/test/DoS_tests.cpp
index 349af79763f2..36146b6b47d8 100644
--- a/src/test/DoS_tests.cpp
+++ b/src/test/DoS_tests.cpp
@@ -17,7 +17,7 @@
 #include "pow.h"
 #include "script/sign.h"
 #include "serialize.h"
-#include "util.h"
+#include "util/system.h"
 #include "validation.h"
 
 #include <stdint.h>
diff --git a/src/test/alert_tests.cpp b/src/test/alert_tests.cpp
index 2a35d3b00bfc..3d478c10bead 100644
--- a/src/test/alert_tests.cpp
+++ b/src/test/alert_tests.cpp
@@ -8,7 +8,7 @@
 //
 
 #include "chainparams.h"
-#include "util.h"
+#include "util/system.h"
 
 #include "test/test_bitcoin.h"
 
diff --git a/src/test/allocator_tests.cpp b/src/test/allocator_tests.cpp
index 9976268ce9c2..c22e21ad92b0 100644
--- a/src/test/allocator_tests.cpp
+++ b/src/test/allocator_tests.cpp
@@ -2,7 +2,7 @@
 // Distributed under the MIT/X11 software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
-#include "util.h"
+#include "util/system.h"
 
 #include "support/allocators/zeroafterfree.h"
 #include "test/test_pivx.h"
diff --git a/src/test/base58_tests.cpp b/src/test/base58_tests.cpp
index 5e907e58ba3b..11b50bbe9f5d 100644
--- a/src/test/base58_tests.cpp
+++ b/src/test/base58_tests.cpp
@@ -12,7 +12,7 @@
 #include "key.h"
 #include "script/script.h"
 #include "uint256.h"
-#include "util.h"
+#include "util/system.h"
 #include "utilstrencodings.h"
 #include "test/test_pivx.h"
 
diff --git a/src/test/bloom_tests.cpp b/src/test/bloom_tests.cpp
index 9b99d10fca7c..63dba3864b0f 100644
--- a/src/test/bloom_tests.cpp
+++ b/src/test/bloom_tests.cpp
@@ -13,7 +13,7 @@
 #include "serialize.h"
 #include "streams.h"
 #include "uint256.h"
-#include "util.h"
+#include "util/system.h"
 #include "utilstrencodings.h"
 #include "test/test_pivx.h"
 
diff --git a/src/test/compress_tests.cpp b/src/test/compress_tests.cpp
index 7dac65943ea6..c0bcbb7ba67b 100644
--- a/src/test/compress_tests.cpp
+++ b/src/test/compress_tests.cpp
@@ -3,7 +3,7 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include "compressor.h"
-#include "util.h"
+#include "util/system.h"
 #include "test/test_pivx.h"
 
 #include <stdint.h>
diff --git a/src/test/dbwrapper_tests.cpp b/src/test/dbwrapper_tests.cpp
index 7da815912b49..d060a03eb8a1 100644
--- a/src/test/dbwrapper_tests.cpp
+++ b/src/test/dbwrapper_tests.cpp
@@ -24,7 +24,7 @@ BOOST_FIXTURE_TEST_SUITE(dbwrapper_tests, BasicTestingSetup)
 BOOST_AUTO_TEST_CASE(dbwrapper)
 {
     {
-        fs::path ph = fs::temp_directory_path() / fs::unique_path();
+        fs::path ph = SetDataDir(std::string("dbwrapper"));
         CDBWrapper dbw(ph, (1 << 20), true, false);
         char key = 'k';
         uint256 in = GetRandHash();
@@ -114,7 +114,7 @@ BOOST_AUTO_TEST_CASE(dbwrapper_basic_data)
 BOOST_AUTO_TEST_CASE(dbwrapper_batch)
 {
     {
-        fs::path ph = fs::temp_directory_path() / fs::unique_path();
+        fs::path ph = SetDataDir(std::string("dbwrapper_batch"));
         CDBWrapper dbw(ph, (1 << 20), true, false);
 
         char key = 'i';
@@ -149,7 +149,7 @@ BOOST_AUTO_TEST_CASE(dbwrapper_batch)
 BOOST_AUTO_TEST_CASE(dbwrapper_iterator)
 {
     {
-        fs::path ph = fs::temp_directory_path() / fs::unique_path();
+        fs::path ph = SetDataDir(std::string("dbwrapper_iterator"));
         CDBWrapper dbw(ph, (1 << 20), true, false);
 
         // The two keys are intentionally chosen for ordering
diff --git a/src/test/flatfile_tests.cpp b/src/test/flatfile_tests.cpp
new file mode 100644
index 000000000000..e02ae7c0cf4b
--- /dev/null
+++ b/src/test/flatfile_tests.cpp
@@ -0,0 +1,123 @@
+// Copyright (c) 2019 The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include "flatfile.h"
+#include "test/test_pivx.h"
+
+#include <boost/test/unit_test.hpp>
+
+BOOST_FIXTURE_TEST_SUITE(flatfile_tests, BasicTestingSetup)
+
+BOOST_AUTO_TEST_CASE(flatfile_filename)
+{
+    auto data_dir = SetDataDir("flatfile_test");
+
+    FlatFilePos pos(456, 789);
+
+    FlatFileSeq seq1(data_dir, "a", 16 * 1024);
+    BOOST_CHECK_EQUAL(seq1.FileName(pos), data_dir / "a00456.dat");
+
+    FlatFileSeq seq2(data_dir / "a", "b", 16 * 1024);
+    BOOST_CHECK_EQUAL(seq2.FileName(pos), data_dir / "a" / "b00456.dat");
+}
+
+BOOST_AUTO_TEST_CASE(flatfile_open)
+{
+    auto data_dir = SetDataDir("flatfile_test");
+    FlatFileSeq seq(data_dir, "a", 16 * 1024);
+
+    std::string line1("A purely peer-to-peer version of electronic cash would allow online "
+                      "payments to be sent directly from one party to another without going "
+                      "through a financial institution.");
+    std::string line2("Digital signatures provide part of the solution, but the main benefits are "
+                      "lost if a trusted third party is still required to prevent double-spending.");
+
+    size_t pos1 = 0;
+    size_t pos2 = pos1 + GetSerializeSize(line1, CLIENT_VERSION);
+
+    // Write first line to file.
+    {
+        CAutoFile file(seq.Open(FlatFilePos(0, pos1)), SER_DISK, CLIENT_VERSION);
+        file << LIMITED_STRING(line1, 256);
+    }
+
+    // Attempt to append to file opened in read-only mode.
+    {
+        CAutoFile file(seq.Open(FlatFilePos(0, pos2), true), SER_DISK, CLIENT_VERSION);
+        BOOST_CHECK_THROW(file << LIMITED_STRING(line2, 256), std::ios_base::failure);
+    }
+
+    // Append second line to file.
+    {
+        CAutoFile file(seq.Open(FlatFilePos(0, pos2)), SER_DISK, CLIENT_VERSION);
+        file << LIMITED_STRING(line2, 256);
+    }
+
+    // Read text from file in read-only mode.
+    {
+        std::string text;
+        CAutoFile file(seq.Open(FlatFilePos(0, pos1), true), SER_DISK, CLIENT_VERSION);
+
+        file >> LIMITED_STRING(text, 256);
+        BOOST_CHECK_EQUAL(text, line1);
+
+        file >> LIMITED_STRING(text, 256);
+        BOOST_CHECK_EQUAL(text, line2);
+    }
+
+    // Read text from file with position offset.
+    {
+        std::string text;
+        CAutoFile file(seq.Open(FlatFilePos(0, pos2)), SER_DISK, CLIENT_VERSION);
+
+        file >> LIMITED_STRING(text, 256);
+        BOOST_CHECK_EQUAL(text, line2);
+    }
+
+    // Ensure another file in the sequence has no data.
+    {
+        std::string text;
+        CAutoFile file(seq.Open(FlatFilePos(1, pos2)), SER_DISK, CLIENT_VERSION);
+        BOOST_CHECK_THROW(file >> LIMITED_STRING(text, 256), std::ios_base::failure);
+    }
+}
+
+BOOST_AUTO_TEST_CASE(flatfile_allocate)
+{
+    auto data_dir = SetDataDir("flatfile_test");
+    FlatFileSeq seq(data_dir, "a", 100);
+
+    bool out_of_space;
+
+    BOOST_CHECK_EQUAL(seq.Allocate(FlatFilePos(0, 0), 1, out_of_space), 100);
+    BOOST_CHECK_EQUAL(fs::file_size(seq.FileName(FlatFilePos(0, 0))), 100);
+    BOOST_CHECK(!out_of_space);
+
+    BOOST_CHECK_EQUAL(seq.Allocate(FlatFilePos(0, 99), 1, out_of_space), 0);
+    BOOST_CHECK_EQUAL(fs::file_size(seq.FileName(FlatFilePos(0, 99))), 100);
+    BOOST_CHECK(!out_of_space);
+
+    BOOST_CHECK_EQUAL(seq.Allocate(FlatFilePos(0, 99), 2, out_of_space), 101);
+    BOOST_CHECK_EQUAL(fs::file_size(seq.FileName(FlatFilePos(0, 99))), 200);
+    BOOST_CHECK(!out_of_space);
+}
+
+BOOST_AUTO_TEST_CASE(flatfile_flush)
+{
+    auto data_dir = SetDataDir("flatfile_test");
+    FlatFileSeq seq(data_dir, "a", 100);
+
+    bool out_of_space;
+    seq.Allocate(FlatFilePos(0, 0), 1, out_of_space);
+
+    // Flush without finalize should not truncate file.
+    seq.Flush(FlatFilePos(0, 1));
+    BOOST_CHECK_EQUAL(fs::file_size(seq.FileName(FlatFilePos(0, 1))), 100);
+
+    // Flush with finalize should truncate file.
+    seq.Flush(FlatFilePos(0, 1), true);
+    BOOST_CHECK_EQUAL(fs::file_size(seq.FileName(FlatFilePos(0, 1))), 1);
+}
+
+BOOST_AUTO_TEST_SUITE_END()
diff --git a/src/test/getarg_tests.cpp b/src/test/getarg_tests.cpp
index 1bc35d541a84..8d0eeb1b6044 100644
--- a/src/test/getarg_tests.cpp
+++ b/src/test/getarg_tests.cpp
@@ -3,7 +3,7 @@
 // Distributed under the MIT/X11 software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
-#include "util.h"
+#include "util/system.h"
 #include "test/test_pivx.h"
 
 #include <string>
diff --git a/src/test/key_tests.cpp b/src/test/key_tests.cpp
index 7cf278d01af2..e33de3fe0f5b 100644
--- a/src/test/key_tests.cpp
+++ b/src/test/key_tests.cpp
@@ -8,7 +8,7 @@
 #include "base58.h"
 #include "script/script.h"
 #include "uint256.h"
-#include "util.h"
+#include "util/system.h"
 #include "utilstrencodings.h"
 #include "test_pivx.h"
 
diff --git a/src/test/librust/wallet_zkeys_tests.cpp b/src/test/librust/wallet_zkeys_tests.cpp
index 2093c9877551..cb06c2efbfa8 100644
--- a/src/test/librust/wallet_zkeys_tests.cpp
+++ b/src/test/librust/wallet_zkeys_tests.cpp
@@ -9,7 +9,7 @@
 #include "sapling/address.h"
 #include "wallet/wallet.h"
 #include "wallet/walletdb.h"
-#include "util.h"
+#include "util/system.h"
 #include <boost/test/unit_test.hpp>
 
 /**
diff --git a/src/test/mempool_tests.cpp b/src/test/mempool_tests.cpp
index 0ca5a76ae982..da62536d506f 100644
--- a/src/test/mempool_tests.cpp
+++ b/src/test/mempool_tests.cpp
@@ -6,7 +6,7 @@
 
 #include "policy/feerate.h"
 #include "txmempool.h"
-#include "util.h"
+#include "util/system.h"
 
 #include <boost/test/unit_test.hpp>
 
diff --git a/src/test/miner_tests.cpp b/src/test/miner_tests.cpp
index a0924ad7d143..317d3d3b1c29 100644
--- a/src/test/miner_tests.cpp
+++ b/src/test/miner_tests.cpp
@@ -11,7 +11,7 @@
 #include "miner.h"
 #include "pubkey.h"
 #include "uint256.h"
-#include "util.h"
+#include "util/system.h"
 #include "validation.h"
 #include "wallet/wallet.h"
 
diff --git a/src/test/policyestimator_tests.cpp b/src/test/policyestimator_tests.cpp
index 9e9e57655985..91f672d52d81 100644
--- a/src/test/policyestimator_tests.cpp
+++ b/src/test/policyestimator_tests.cpp
@@ -6,7 +6,7 @@
 #include "policy/fees.h"
 #include "txmempool.h"
 #include "uint256.h"
-#include "util.h"
+#include "util/system.h"
 
 #include "test/test_pivx.h"
 
diff --git a/src/test/rpc_tests.cpp b/src/test/rpc_tests.cpp
index 042c2316cfed..9a5cb364098f 100644
--- a/src/test/rpc_tests.cpp
+++ b/src/test/rpc_tests.cpp
@@ -8,7 +8,7 @@
 
 #include "base58.h"
 #include "netbase.h"
-#include "util.h"
+#include "util/system.h"
 
 #include "test/test_pivx.h"
 
diff --git a/src/test/sighash_tests.cpp b/src/test/sighash_tests.cpp
index 79ebc1aaad1a..458cc4439fa5 100644
--- a/src/test/sighash_tests.cpp
+++ b/src/test/sighash_tests.cpp
@@ -11,7 +11,7 @@
 #include "serialize.h"
 #include "script/script.h"
 #include "script/interpreter.h"
-#include "util.h"
+#include "util/system.h"
 #include "validation.h"
 #include "version.h"
 
diff --git a/src/test/skiplist_tests.cpp b/src/test/skiplist_tests.cpp
index 17ff327de683..e8385f1e2b0d 100644
--- a/src/test/skiplist_tests.cpp
+++ b/src/test/skiplist_tests.cpp
@@ -5,7 +5,7 @@
 
 #include "test/test_pivx.h"
 
-#include "util.h"
+#include "util/system.h"
 #include "validation.h"
 
 #include <vector>
diff --git a/src/test/test_pivx.cpp b/src/test/test_pivx.cpp
index 732fce7474d6..a120ac67ea08 100644
--- a/src/test/test_pivx.cpp
+++ b/src/test/test_pivx.cpp
@@ -39,29 +39,38 @@ std::ostream& operator<<(std::ostream& os, const uint256& num)
 }
 
 BasicTestingSetup::BasicTestingSetup(const std::string& chainName)
+    : m_path_root(fs::temp_directory_path() / "test_pivx" / strprintf("%lu_%i", (unsigned long)GetTime(), (int)(InsecureRandRange(1 << 30))))
 {
-        ECC_Start();
-        SetupEnvironment();
-        InitSignatureCache();
-        fCheckBlockIndex = true;
-        SelectParams(chainName);
-        evoDb.reset(new CEvoDB(1 << 20, true, true));
-        deterministicMNManager.reset(new CDeterministicMNManager(*evoDb));
+    ECC_Start();
+    SetupEnvironment();
+    InitSignatureCache();
+    fCheckBlockIndex = true;
+    SelectParams(chainName);
+    evoDb.reset(new CEvoDB(1 << 20, true, true));
+    deterministicMNManager.reset(new CDeterministicMNManager(*evoDb));
 }
+
 BasicTestingSetup::~BasicTestingSetup()
 {
-        ECC_Stop();
-        g_connman.reset();
-        deterministicMNManager.reset();
-        evoDb.reset();
+    fs::remove_all(m_path_root);
+    ECC_Stop();
+    g_connman.reset();
+    deterministicMNManager.reset();
+    evoDb.reset();
+}
+
+fs::path BasicTestingSetup::SetDataDir(const std::string& name)
+{
+    fs::path ret = m_path_root / name;
+    fs::create_directories(ret);
+    gArgs.ForceSetArg("-datadir", ret.string());
+    return ret;
 }
 
 TestingSetup::TestingSetup(const std::string& chainName) : BasicTestingSetup(chainName)
 {
+        SetDataDir("tempdir");
         ClearDatadirCache();
-        pathTemp = fs::temp_directory_path() / strprintf("test_pivx_%lu_%i", (unsigned long)GetTime(), (int)(InsecureRandRange(100000)));
-        fs::create_directories(pathTemp);
-        gArgs.ForceSetArg("-datadir", pathTemp.string());
 
         // Start the lightweight task scheduler thread
         CScheduler::Function serviceLoop = std::bind(&CScheduler::serviceQueue, &scheduler);
@@ -110,7 +119,6 @@ TestingSetup::~TestingSetup()
         delete pblocktree;
         delete zerocoinDB;
         delete pSporkDB;
-        fs::remove_all(pathTemp);
 }
 
 // Test chain only available on regtest
diff --git a/src/test/test_pivx.h b/src/test/test_pivx.h
index 67ed4d039377..75c85e60629a 100644
--- a/src/test/test_pivx.h
+++ b/src/test/test_pivx.h
@@ -38,6 +38,11 @@ struct BasicTestingSetup {
 
     BasicTestingSetup(const std::string& chainName = CBaseChainParams::MAIN);
     ~BasicTestingSetup();
+
+    fs::path SetDataDir(const std::string& name);
+
+private:
+    const fs::path m_path_root;
 };
 
 /** Testing setup that configures a complete environment.
@@ -47,7 +52,6 @@ struct BasicTestingSetup {
 class CConnman;
 struct TestingSetup: public BasicTestingSetup {
     CCoinsViewDB *pcoinsdbview;
-    fs::path pathTemp;
     boost::thread_group threadGroup;
     CConnman* connman;
     CScheduler scheduler;
diff --git a/src/test/util_tests.cpp b/src/test/util_tests.cpp
index c5774015c720..a66a1ffa7285 100644
--- a/src/test/util_tests.cpp
+++ b/src/test/util_tests.cpp
@@ -3,7 +3,7 @@
 // Distributed under the MIT/X11 software license, see the accompanying
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
-#include "util.h"
+#include "util/system.h"
 
 #include "clientversion.h"
 #include "primitives/transaction.h"
diff --git a/src/timedata.cpp b/src/timedata.cpp
index 4963fbdeaac6..e29cfcad0c96 100644
--- a/src/timedata.cpp
+++ b/src/timedata.cpp
@@ -9,7 +9,7 @@
 #include "guiinterface.h"
 #include "netaddress.h"
 #include "sync.h"
-#include "util.h"
+#include "util/system.h"
 #include "warnings.h"
 
 
diff --git a/src/torcontrol.cpp b/src/torcontrol.cpp
index c0439091852c..38bbe9b38df8 100644
--- a/src/torcontrol.cpp
+++ b/src/torcontrol.cpp
@@ -10,7 +10,7 @@
 #include "utilstrencodings.h"
 #include "netbase.h"
 #include "net.h"
-#include "util.h"
+#include "util/system.h"
 #include "crypto/hmac_sha256.h"
 
 #include <vector>
diff --git a/src/txdb.cpp b/src/txdb.cpp
index 4862fcbf9412..42c45ffcc3dd 100644
--- a/src/txdb.cpp
+++ b/src/txdb.cpp
@@ -9,7 +9,7 @@
 #include "random.h"
 #include "pow.h"
 #include "uint256.h"
-#include "util.h"
+#include "util/system.h"
 #include "zpiv/zerocoin.h"
 
 #include <stdint.h>
diff --git a/src/txdb.h b/src/txdb.h
index ed04c4b97b83..48ce71047976 100644
--- a/src/txdb.h
+++ b/src/txdb.h
@@ -32,7 +32,7 @@ static const int64_t nMaxDbCache = sizeof(void*) > 4 ? 16384 : 1024;
 //! min. -dbcache in (MiB)
 static const int64_t nMinDbCache = 4;
 
-struct CDiskTxPos : public CDiskBlockPos
+struct CDiskTxPos : public FlatFilePos
 {
     unsigned int nTxOffset; // after header
 
@@ -41,11 +41,11 @@ struct CDiskTxPos : public CDiskBlockPos
     template <typename Stream, typename Operation>
     inline void SerializationOp(Stream& s, Operation ser_action)
     {
-        READWRITEAS(CDiskBlockPos, *this);
+        READWRITEAS(FlatFilePos, *this);
         READWRITE(VARINT(nTxOffset));
     }
 
-    CDiskTxPos(const CDiskBlockPos& blockIn, unsigned int nTxOffsetIn) : CDiskBlockPos(blockIn.nFile, blockIn.nPos), nTxOffset(nTxOffsetIn)
+    CDiskTxPos(const FlatFilePos& blockIn, unsigned int nTxOffsetIn) : FlatFilePos(blockIn.nFile, blockIn.nPos), nTxOffset(nTxOffsetIn)
     {
     }
 
@@ -56,7 +56,7 @@ struct CDiskTxPos : public CDiskBlockPos
 
     void SetNull()
     {
-        CDiskBlockPos::SetNull();
+        FlatFilePos::SetNull();
         nTxOffset = 0;
     }
 };
diff --git a/src/txmempool.cpp b/src/txmempool.cpp
index 42c8ff5bb93f..e279bb679c61 100644
--- a/src/txmempool.cpp
+++ b/src/txmempool.cpp
@@ -14,7 +14,7 @@
 #include "reverse_iterate.h"
 #include "streams.h"
 #include "timedata.h"
-#include "util.h"
+#include "util/system.h"
 #include "utilmoneystr.h"
 #include "utiltime.h"
 #include "version.h"
diff --git a/src/util.cpp b/src/util/system.cpp
similarity index 99%
rename from src/util.cpp
rename to src/util/system.cpp
index a4bcb85ea9f8..bc7085985c45 100644
--- a/src/util.cpp
+++ b/src/util/system.cpp
@@ -9,7 +9,7 @@
 #include "config/pivx-config.h"
 #endif
 
-#include "util.h"
+#include "util/system.h"
 
 #include "chainparamsbase.h"
 #include "random.h"
@@ -95,6 +95,14 @@ ArgsManager gArgs;
 bool fDaemon = false;
 CTranslationInterface translationInterface;
 
+bool CheckDiskSpace(const fs::path& dir, uint64_t additional_bytes)
+{
+    constexpr uint64_t min_disk_space = 52428800; // 50 MiB
+
+    uint64_t free_bytes_available = fs::space(dir).available;
+    return free_bytes_available >= min_disk_space + additional_bytes;
+}
+
 /**
  * Interpret a string argument as a boolean.
  *
diff --git a/src/util.h b/src/util/system.h
similarity index 98%
rename from src/util.h
rename to src/util/system.h
index ee5bfe9ba1db..8837ee8784bf 100644
--- a/src/util.h
+++ b/src/util/system.h
@@ -9,8 +9,8 @@
  * Server/client environment: argument handling, config file parsing,
  * thread wrappers
  */
-#ifndef BITCOIN_UTIL_H
-#define BITCOIN_UTIL_H
+#ifndef BITCOIN_UTIL_SYSTEM_H
+#define BITCOIN_UTIL_SYSTEM_H
 
 #if defined(HAVE_CONFIG_H)
 #include "config/pivx-config.h"
@@ -86,6 +86,7 @@ bool FileCommit(FILE* file);
 bool TruncateFile(FILE* file, unsigned int length);
 int RaiseFileDescriptorLimit(int nMinFD);
 void AllocateFileRange(FILE* file, unsigned int offset, unsigned int length);
+bool CheckDiskSpace(const fs::path& dir, uint64_t additional_bytes = 0);
 bool RenameOver(fs::path src, fs::path dest);
 bool TryCreateDirectories(const fs::path& p);
 fs::path GetDefaultDataDir();
@@ -292,4 +293,4 @@ fs::path AbsPathForConfigVal(const fs::path& path, bool net_specific = true);
  */
 int ScheduleBatchPriority(void);
 
-#endif // BITCOIN_UTIL_H
+#endif // BITCOIN_UTIL_SYSTEM_H
diff --git a/src/validation.cpp b/src/validation.cpp
index db625a30b883..f7409d10b46c 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -24,6 +24,7 @@
 #include "consensus/zerocoin_verify.h"
 #include "evo/deterministicmns.h"
 #include "evo/specialtx.h"
+#include "flatfile.h"
 #include "fs.h"
 #include "guiinterface.h"
 #include "init.h"
@@ -34,13 +35,9 @@
 #include "masternode-payments.h"
 #include "masternode-sync.h"
 #include "masternodeman.h"
-#include "messagesigner.h"
-#include "netmessagemaker.h"
-#include "net_processing.h"
 #include "policy/policy.h"
 #include "pow.h"
 #include "reverse_iterate.h"
-#include "sapling/sapling_validation.h"
 #include "script/sigcache.h"
 #include "spork.h"
 #include "sporkdb.h"
@@ -48,7 +45,7 @@
 #include "txdb.h"
 #include "txmempool.h"
 #include "undo.h"
-#include "util.h"
+#include "util/system.h"
 #include "utilmoneystr.h"
 #include "validationinterface.h"
 #include "warnings.h"
@@ -224,6 +221,8 @@ enum FlushStateMode {
 
 // See definition for documentation
 bool static FlushStateToDisk(CValidationState &state, FlushStateMode mode);
+static FlatFileSeq BlockFileSeq();
+static FlatFileSeq UndoFileSeq();
 
 bool CheckFinalTx(const CTransactionRef& tx, int flags)
 {
@@ -780,7 +779,7 @@ bool GetTransaction(const uint256& hash, CTransactionRef& txOut, uint256& hashBl
 // CBlock and CBlockIndex
 //
 
-bool WriteBlockToDisk(const CBlock& block, CDiskBlockPos& pos)
+bool WriteBlockToDisk(const CBlock& block, FlatFilePos& pos)
 {
     // Open history file to append
     CAutoFile fileout(OpenBlockFile(pos), SER_DISK, CLIENT_VERSION);
@@ -801,7 +800,7 @@ bool WriteBlockToDisk(const CBlock& block, CDiskBlockPos& pos)
     return true;
 }
 
-bool ReadBlockFromDisk(CBlock& block, const CDiskBlockPos& pos)
+bool ReadBlockFromDisk(CBlock& block, const FlatFilePos& pos)
 {
     block.SetNull();
 
@@ -828,7 +827,7 @@ bool ReadBlockFromDisk(CBlock& block, const CDiskBlockPos& pos)
 
 bool ReadBlockFromDisk(CBlock& block, const CBlockIndex* pindex)
 {
-    CDiskBlockPos blockPos = WITH_LOCK(cs_main, return pindex->GetBlockPos(); );
+    FlatFilePos blockPos = WITH_LOCK(cs_main, return pindex->GetBlockPos(); );
     if (!ReadBlockFromDisk(block, blockPos)) {
         return false;
     }
@@ -1219,7 +1218,7 @@ static bool AbortNode(CValidationState& state, const std::string& strMessage, co
 
 namespace {
 
-bool UndoWriteToDisk(const CBlockUndo& blockundo, CDiskBlockPos& pos, const uint256& hashBlock)
+bool UndoWriteToDisk(const CBlockUndo& blockundo, FlatFilePos& pos, const uint256& hashBlock)
 {
     // Open history file to append
     CAutoFile fileout(OpenUndoFile(pos), SER_DISK, CLIENT_VERSION);
@@ -1246,7 +1245,7 @@ bool UndoWriteToDisk(const CBlockUndo& blockundo, CDiskBlockPos& pos, const uint
     return true;
 }
 
-bool UndoReadFromDisk(CBlockUndo& blockundo, const CDiskBlockPos& pos, const uint256& hashBlock)
+bool UndoReadFromDisk(CBlockUndo& blockundo, const FlatFilePos& pos, const uint256& hashBlock)
 {
     // Open history file to read
     CAutoFile filein(OpenUndoFile(pos, true), SER_DISK, CLIENT_VERSION);
@@ -1333,7 +1332,7 @@ DisconnectResult DisconnectBlock(CBlock& block, const CBlockIndex* pindex, CCoin
     bool fClean = true;
 
     CBlockUndo blockUndo;
-    CDiskBlockPos pos = pindex->GetUndoPos();
+    FlatFilePos pos = pindex->GetUndoPos();
     if (pos.IsNull()) {
         error("%s: no undo data available", __func__);
         return DISCONNECT_FAILED;
@@ -1430,31 +1429,18 @@ void static FlushBlockFile(bool fFinalize = false)
 {
     LOCK(cs_LastBlockFile);
 
-    CDiskBlockPos posOld(nLastBlockFile, 0);
-    bool status = true;
-
-    FILE* fileOld = OpenBlockFile(posOld);
-    if (fileOld) {
-        if (fFinalize)
-            status &= TruncateFile(fileOld, vinfoBlockFile[nLastBlockFile].nSize);
-        status &= FileCommit(fileOld);
-        fclose(fileOld);
-    }
-
-    fileOld = OpenUndoFile(posOld);
-    if (fileOld) {
-        if (fFinalize)
-            status &= TruncateFile(fileOld, vinfoBlockFile[nLastBlockFile].nUndoSize);
-        status &= FileCommit(fileOld);
-        fclose(fileOld);
-    }
+    FlatFilePos block_pos_old(nLastBlockFile, vinfoBlockFile[nLastBlockFile].nSize);
+    FlatFilePos undo_pos_old(nLastBlockFile, vinfoBlockFile[nLastBlockFile].nUndoSize);
 
+    bool status = true;
+    status &= BlockFileSeq().Flush(block_pos_old, fFinalize);
+    status &= UndoFileSeq().Flush(undo_pos_old, fFinalize);
     if (!status) {
         AbortNode("Flushing block file to disk failed. This is likely the result of an I/O error.");
     }
 }
 
-bool FindUndoPos(CValidationState& state, int nFile, CDiskBlockPos& pos, unsigned int nAddSize);
+bool FindUndoPos(CValidationState& state, int nFile, FlatFilePos& pos, unsigned int nAddSize);
 
 static CCheckQueue<CScriptCheck> scriptcheckqueue(128);
 
@@ -1760,7 +1746,7 @@ static bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockInd
     // Write undo information to disk
     if (pindex->GetUndoPos().IsNull() || !pindex->IsValid(BLOCK_VALID_SCRIPTS)) {
         if (pindex->GetUndoPos().IsNull()) {
-            CDiskBlockPos diskPosBlock;
+            FlatFilePos diskPosBlock;
             if (!FindUndoPos(state, pindex->nFile, diskPosBlock, ::GetSerializeSize(blockundo, SER_DISK, CLIENT_VERSION) + 40))
                 return error("ConnectBlock() : FindUndoPos failed");
             if (!UndoWriteToDisk(blockundo, diskPosBlock, pindex->pprev->GetBlockHash()))
@@ -1853,8 +1839,9 @@ bool static FlushStateToDisk(CValidationState& state, FlushStateMode mode)
         // Write blocks and block index to disk.
         if (fDoFullFlush || fPeriodicWrite) {
             // Depend on nMinDiskSpace to ensure we can write block index
-            if (!CheckDiskSpace(0, true))
-                return state.Error("out of disk space");
+            if (!CheckDiskSpace(GetBlocksDir())) {
+                return AbortNode(state, "Disk space is low!", _("Error: Disk space is low!"));
+            }
             // First make sure all block and undo data is flushed to disk.
             FlushBlockFile();
             // Then update all block file information (which may refer to block and undo files).
@@ -1885,8 +1872,9 @@ bool static FlushStateToDisk(CValidationState& state, FlushStateMode mode)
             // twice (once in the log, and once in the tables). This is already
             // an overestimation, as most will delete an existing entry or
             // overwrite one. Still, use a conservative safety factor of 2.
-            if (!CheckDiskSpace(48 * 2 * 2 * pcoinsTip->GetCacheSize()))
-                return state.Error("out of disk space");
+            if (!CheckDiskSpace(GetDataDir(), 48 * 2 * 2 * pcoinsTip->GetCacheSize())) {
+                return AbortNode(state, "Disk space is low!", _("Error: Disk space is low!"));
+            }
             // Flush the chainstate (which may refer to block index entries).
             if (!pcoinsTip->Flush())
                 return AbortNode(state, "Failed to write to coin database");
@@ -2555,7 +2543,7 @@ CBlockIndex* AddToBlockIndex(const CBlock& block)
 }
 
 /** Mark a block as having its data received and checked (up to BLOCK_VALID_TRANSACTIONS). */
-bool ReceivedBlockTransactions(const CBlock& block, CValidationState& state, CBlockIndex* pindexNew, const CDiskBlockPos& pos)
+bool ReceivedBlockTransactions(const CBlock& block, CValidationState& state, CBlockIndex* pindexNew, const FlatFilePos& pos)
 {
     if (block.IsProofOfStake())
         pindexNew->SetProofOfStake();
@@ -2621,7 +2609,7 @@ bool ReceivedBlockTransactions(const CBlock& block, CValidationState& state, CBl
     return true;
 }
 
-bool FindBlockPos(CValidationState& state, CDiskBlockPos& pos, unsigned int nAddSize, unsigned int nHeight, uint64_t nTime, bool fKnown = false)
+bool FindBlockPos(CValidationState& state, FlatFilePos& pos, unsigned int nAddSize, unsigned int nHeight, uint64_t nTime, bool fKnown = false)
 {
     LOCK(cs_LastBlockFile);
 
@@ -2656,49 +2644,34 @@ bool FindBlockPos(CValidationState& state, CDiskBlockPos& pos, unsigned int nAdd
         vinfoBlockFile[nFile].nSize += nAddSize;
 
     if (!fKnown) {
-        unsigned int nOldChunks = (pos.nPos + BLOCKFILE_CHUNK_SIZE - 1) / BLOCKFILE_CHUNK_SIZE;
-        unsigned int nNewChunks = (vinfoBlockFile[nFile].nSize + BLOCKFILE_CHUNK_SIZE - 1) / BLOCKFILE_CHUNK_SIZE;
-        if (nNewChunks > nOldChunks) {
-            if (CheckDiskSpace(nNewChunks * BLOCKFILE_CHUNK_SIZE - pos.nPos, true)) {
-                FILE* file = OpenBlockFile(pos);
-                if (file) {
-                    LogPrintf("Pre-allocating up to position 0x%x in blk%05u.dat\n", nNewChunks * BLOCKFILE_CHUNK_SIZE, pos.nFile);
-                    AllocateFileRange(file, pos.nPos, nNewChunks * BLOCKFILE_CHUNK_SIZE - pos.nPos);
-                    fclose(file);
-                }
-            } else
-                return state.Error("out of disk space");
+        bool out_of_space;
+        BlockFileSeq().Allocate(pos, nAddSize, out_of_space);
+        if (out_of_space) {
+            return AbortNode("Disk space is low!", _("Error: Disk space is low!"));
         }
+        // future: add prunning flag check
     }
 
     setDirtyFileInfo.insert(nFile);
     return true;
 }
 
-bool FindUndoPos(CValidationState& state, int nFile, CDiskBlockPos& pos, unsigned int nAddSize)
+bool FindUndoPos(CValidationState& state, int nFile, FlatFilePos& pos, unsigned int nAddSize)
 {
     pos.nFile = nFile;
 
     LOCK(cs_LastBlockFile);
 
-    unsigned int nNewSize;
     pos.nPos = vinfoBlockFile[nFile].nUndoSize;
-    nNewSize = vinfoBlockFile[nFile].nUndoSize += nAddSize;
+    vinfoBlockFile[nFile].nUndoSize += nAddSize;
     setDirtyFileInfo.insert(nFile);
 
-    unsigned int nOldChunks = (pos.nPos + UNDOFILE_CHUNK_SIZE - 1) / UNDOFILE_CHUNK_SIZE;
-    unsigned int nNewChunks = (nNewSize + UNDOFILE_CHUNK_SIZE - 1) / UNDOFILE_CHUNK_SIZE;
-    if (nNewChunks > nOldChunks) {
-        if (CheckDiskSpace(nNewChunks * UNDOFILE_CHUNK_SIZE - pos.nPos, true)) {
-            FILE* file = OpenUndoFile(pos);
-            if (file) {
-                LogPrintf("Pre-allocating up to position 0x%x in rev%05u.dat\n", nNewChunks * UNDOFILE_CHUNK_SIZE, pos.nFile);
-                AllocateFileRange(file, pos.nPos, nNewChunks * UNDOFILE_CHUNK_SIZE - pos.nPos);
-                fclose(file);
-            }
-        } else
-            return state.Error("out of disk space");
+    bool out_of_space;
+    UndoFileSeq().Allocate(pos, nAddSize, out_of_space);
+    if (out_of_space) {
+        return AbortNode(state, "Disk space is low!", _("Error: Disk space is low!"));
     }
+    // future: add prunning flag check
 
     return true;
 }
@@ -3149,7 +3122,7 @@ bool AcceptBlockHeader(const CBlock& block, CValidationState& state, CBlockIndex
     return true;
 }
 
-bool AcceptBlock(const CBlock& block, CValidationState& state, CBlockIndex** ppindex, CDiskBlockPos* dbp)
+bool AcceptBlock(const CBlock& block, CValidationState& state, CBlockIndex** ppindex, FlatFilePos* dbp)
 {
     AssertLockHeld(cs_main);
 
@@ -3378,7 +3351,7 @@ bool AcceptBlock(const CBlock& block, CValidationState& state, CBlockIndex** ppi
     // Write block to history file
     try {
         unsigned int nBlockSize = ::GetSerializeSize(block, SER_DISK, CLIENT_VERSION);
-        CDiskBlockPos blockPos;
+        FlatFilePos blockPos;
         if (dbp != NULL)
             blockPos = *dbp;
         if (!FindBlockPos(state, blockPos, nBlockSize + 8, nHeight, block.GetBlockTime(), dbp != NULL))
@@ -3395,7 +3368,7 @@ bool AcceptBlock(const CBlock& block, CValidationState& state, CBlockIndex** ppi
     return true;
 }
 
-bool ProcessNewBlock(CValidationState& state, CNode* pfrom, const std::shared_ptr<const CBlock> pblock, CDiskBlockPos* dbp, bool* fAccepted)
+bool ProcessNewBlock(CValidationState& state, CNode* pfrom, const std::shared_ptr<const CBlock> pblock, FlatFilePos* dbp, bool* fAccepted)
 {
     AssertLockNotHeld(cs_main);
 
@@ -3469,53 +3442,29 @@ bool TestBlockValidity(CValidationState& state, const CBlock& block, CBlockIndex
     return true;
 }
 
-bool CheckDiskSpace(uint64_t nAdditionalBytes, bool blocks_dir)
+static FlatFileSeq BlockFileSeq()
 {
-    uint64_t nFreeBytesAvailable = fs::space(blocks_dir ? GetBlocksDir() : GetDataDir()).available;
-
-    // Check for nMinDiskSpace bytes (currently 50MB)
-    if (nFreeBytesAvailable < nMinDiskSpace + nAdditionalBytes)
-        return AbortNode("Disk space is low!", _("Error: Disk space is low!"));
-
-    return true;
+    return FlatFileSeq(GetBlocksDir(), "blk", BLOCKFILE_CHUNK_SIZE);
 }
 
-FILE* OpenDiskFile(const CDiskBlockPos& pos, const char* prefix, bool fReadOnly)
+static FlatFileSeq UndoFileSeq()
 {
-    if (pos.IsNull())
-        return NULL;
-    fs::path path = GetBlockPosFilename(pos, prefix);
-    fs::create_directories(path.parent_path());
-    FILE* file = fsbridge::fopen(path, "rb+");
-    if (!file && !fReadOnly)
-        file = fsbridge::fopen(path, "wb+");
-    if (!file) {
-        LogPrintf("Unable to open file %s\n", path.string());
-        return NULL;
-    }
-    if (pos.nPos) {
-        if (fseek(file, pos.nPos, SEEK_SET)) {
-            LogPrintf("Unable to seek to position %u of %s\n", pos.nPos, path.string());
-            fclose(file);
-            return NULL;
-        }
-    }
-    return file;
+    return FlatFileSeq(GetBlocksDir(), "rev", UNDOFILE_CHUNK_SIZE);
 }
 
-FILE* OpenBlockFile(const CDiskBlockPos& pos, bool fReadOnly)
+FILE* OpenBlockFile(const FlatFilePos& pos, bool fReadOnly)
 {
-    return OpenDiskFile(pos, "blk", fReadOnly);
+    return BlockFileSeq().Open(pos, fReadOnly);
 }
 
-FILE* OpenUndoFile(const CDiskBlockPos& pos, bool fReadOnly)
+FILE* OpenUndoFile(const FlatFilePos& pos, bool fReadOnly)
 {
-    return OpenDiskFile(pos, "rev", fReadOnly);
+    return UndoFileSeq().Open(pos, fReadOnly);
 }
 
-fs::path GetBlockPosFilename(const CDiskBlockPos& pos, const char* prefix)
+fs::path GetBlockPosFilename(const FlatFilePos &pos)
 {
-    return GetBlocksDir() / strprintf("%s%05u.dat", prefix, pos.nFile);
+    return BlockFileSeq().FileName(pos);
 }
 
 CBlockIndex* InsertBlockIndex(uint256 hash)
@@ -3619,7 +3568,7 @@ bool static LoadBlockIndexDB(std::string& strError)
         }
     }
     for (std::set<int>::iterator it = setBlkDataFiles.begin(); it != setBlkDataFiles.end(); it++) {
-        CDiskBlockPos pos(*it, 0);
+        FlatFilePos pos(*it, 0);
         if (CAutoFile(OpenBlockFile(pos, true), SER_DISK, CLIENT_VERSION).IsNull()) {
             return false;
         }
@@ -3728,7 +3677,7 @@ bool CVerifyDB::VerifyDB(CCoinsView* coinsview, int nCheckLevel, int nCheckDepth
         // check level 2: verify undo validity
         if (nCheckLevel >= 2 && pindex) {
             CBlockUndo undo;
-            CDiskBlockPos pos = pindex->GetUndoPos();
+            FlatFilePos pos = pindex->GetUndoPos();
             if (!pos.IsNull()) {
                 if (!UndoReadFromDisk(undo, pos, pindex->pprev->GetBlockHash()))
                     return error("%s: *** found bad undo data at %d, hash=%s\n", __func__, pindex->nHeight, pindex->GetBlockHash().ToString());
@@ -3932,7 +3881,7 @@ bool LoadGenesisBlock()
         CBlock& block = const_cast<CBlock&>(Params().GenesisBlock());
         // Start new block file
         unsigned int nBlockSize = ::GetSerializeSize(block, SER_DISK, CLIENT_VERSION);
-        CDiskBlockPos blockPos;
+        FlatFilePos blockPos;
         CValidationState state;
         if (!FindBlockPos(state, blockPos, nBlockSize + 8, 0, block.GetBlockTime()))
             return error("%s: FindBlockPos failed", __func__);
@@ -3949,10 +3898,10 @@ bool LoadGenesisBlock()
 }
 
 
-bool LoadExternalBlockFile(FILE* fileIn, CDiskBlockPos* dbp)
+bool LoadExternalBlockFile(FILE* fileIn, FlatFilePos* dbp)
 {
     // Map of disk positions for blocks with unknown parent (only used for reindex)
-    static std::multimap<uint256, CDiskBlockPos> mapBlocksUnknownParent;
+    static std::multimap<uint256, FlatFilePos> mapBlocksUnknownParent;
     int64_t nStart = GetTimeMillis();
 
     int nLoaded = 0;
@@ -4022,9 +3971,9 @@ bool LoadExternalBlockFile(FILE* fileIn, CDiskBlockPos* dbp)
                 while (!queue.empty()) {
                     uint256 head = queue.front();
                     queue.pop_front();
-                    std::pair<std::multimap<uint256, CDiskBlockPos>::iterator, std::multimap<uint256, CDiskBlockPos>::iterator> range = mapBlocksUnknownParent.equal_range(head);
+                    std::pair<std::multimap<uint256, FlatFilePos>::iterator, std::multimap<uint256, FlatFilePos>::iterator> range = mapBlocksUnknownParent.equal_range(head);
                     while (range.first != range.second) {
-                        std::multimap<uint256, CDiskBlockPos>::iterator it = range.first;
+                        std::multimap<uint256, FlatFilePos>::iterator it = range.first;
                         if (ReadBlockFromDisk(block, it->second)) {
                             LogPrintf("%s: Processing out of order child %s of %s\n", __func__, block.GetHash().ToString(),
                                 head.ToString());
diff --git a/src/validation.h b/src/validation.h
index 46243099ac4a..2f475d8176b5 100644
--- a/src/validation.h
+++ b/src/validation.h
@@ -159,9 +159,6 @@ extern CMoneySupply MoneySupply;
 /** Best header we've seen so far (used for getheaders queries' starting points). */
 extern CBlockIndex* pindexBestHeader;
 
-/** Minimum disk space required - used in CheckDiskSpace() */
-static const uint64_t nMinDiskSpace = 52428800;
-
 /**
  * Process an incoming block. This only returns after the best known valid
  * block is made active. Note that it does not, however, guarantee that the
@@ -174,17 +171,16 @@ static const uint64_t nMinDiskSpace = 52428800;
  * @param[out]  fAccepted  Whether the block is accepted or not
  * @return True if state.IsValid()
  */
-bool ProcessNewBlock(CValidationState& state, CNode* pfrom, const std::shared_ptr<const CBlock> pblock, CDiskBlockPos* dbp, bool* fAccepted = nullptr);
-/** Check whether enough disk space is available for an incoming block */
-bool CheckDiskSpace(uint64_t nAdditionalBytes = 0, bool blocks_dir = false);
+bool ProcessNewBlock(CValidationState& state, CNode* pfrom, const std::shared_ptr<const CBlock> pblock, FlatFilePos* dbp, bool* fAccepted = nullptr);
+
 /** Open a block file (blk?????.dat) */
-FILE* OpenBlockFile(const CDiskBlockPos& pos, bool fReadOnly = false);
+FILE* OpenBlockFile(const FlatFilePos& pos, bool fReadOnly = false);
 /** Open an undo file (rev?????.dat) */
-FILE* OpenUndoFile(const CDiskBlockPos& pos, bool fReadOnly = false);
+FILE* OpenUndoFile(const FlatFilePos& pos, bool fReadOnly = false);
 /** Translation to a filesystem path */
-fs::path GetBlockPosFilename(const CDiskBlockPos& pos, const char* prefix);
+fs::path GetBlockPosFilename(const FlatFilePos &pos);
 /** Import blocks from an external file */
-bool LoadExternalBlockFile(FILE* fileIn, CDiskBlockPos* dbp = NULL);
+bool LoadExternalBlockFile(FILE* fileIn, FlatFilePos* dbp = NULL);
 /** Ensures we have a genesis block in the block tree, possibly writing one to disk. */
 bool LoadGenesisBlock();
 /** Load the block tree and coins database from disk,
@@ -325,8 +321,8 @@ class CScriptCheck
 
 
 /** Functions for disk access for blocks */
-bool WriteBlockToDisk(const CBlock& block, CDiskBlockPos& pos);
-bool ReadBlockFromDisk(CBlock& block, const CDiskBlockPos& pos);
+bool WriteBlockToDisk(const CBlock& block, FlatFilePos& pos);
+bool ReadBlockFromDisk(CBlock& block, const FlatFilePos& pos);
 bool ReadBlockFromDisk(CBlock& block, const CBlockIndex* pindex);
 
 
@@ -344,7 +340,7 @@ bool ContextualCheckBlock(const CBlock& block, CValidationState& state, CBlockIn
 bool TestBlockValidity(CValidationState& state, const CBlock& block, CBlockIndex* pindexPrev, bool fCheckPOW = true, bool fCheckMerkleRoot = true, bool fCheckBlockSig = true);
 
 /** Store block on disk. If dbp is provided, the file is known to already reside on disk */
-bool AcceptBlock(const CBlock& block, CValidationState& state, CBlockIndex** pindex, CDiskBlockPos* dbp = NULL);
+bool AcceptBlock(const CBlock& block, CValidationState& state, CBlockIndex** pindex, FlatFilePos* dbp = NULL);
 bool AcceptBlockHeader(const CBlock& block, CValidationState& state, CBlockIndex** ppindex = nullptr, CBlockIndex* pindexPrev = nullptr);
 
 
diff --git a/src/wallet/db.cpp b/src/wallet/db.cpp
index 94b85583c139..7ea9dfbab1e8 100644
--- a/src/wallet/db.cpp
+++ b/src/wallet/db.cpp
@@ -10,7 +10,7 @@
 #include "guiinterfaceutil.h"
 #include "hash.h"
 #include "protocol.h"
-#include "util.h"
+#include "util/system.h"
 #include "utilstrencodings.h"
 
 #include <stdint.h>
diff --git a/src/wallet/hdchain.cpp b/src/wallet/hdchain.cpp
index 29e37b4fb69e..642fb8217e9a 100644
--- a/src/wallet/hdchain.cpp
+++ b/src/wallet/hdchain.cpp
@@ -7,7 +7,7 @@
 #include "base58.h"
 #include "chainparams.h"
 #include "tinyformat.h"
-#include "util.h"
+#include "util/system.h"
 #include "utilstrencodings.h"
 
 bool CHDChain::SetNull()
diff --git a/src/wallet/rpcdump.cpp b/src/wallet/rpcdump.cpp
index d2af3d405655..f476efde8d24 100644
--- a/src/wallet/rpcdump.cpp
+++ b/src/wallet/rpcdump.cpp
@@ -12,7 +12,7 @@
 #include "script/script.h"
 #include "script/standard.h"
 #include "sync.h"
-#include "util.h"
+#include "util/system.h"
 #include "utilstrencodings.h"
 #include "utiltime.h"
 #include "wallet/wallet.h"
diff --git a/src/wallet/rpcwallet.cpp b/src/wallet/rpcwallet.cpp
index e75e86d20939..43ccaf5ff13f 100644
--- a/src/wallet/rpcwallet.cpp
+++ b/src/wallet/rpcwallet.cpp
@@ -18,7 +18,7 @@
 #include "policy/feerate.h"
 #include "rpc/server.h"
 #include "timedata.h"
-#include "util.h"
+#include "util/system.h"
 #include "utilmoneystr.h"
 #include "wallet.h"
 #include "walletdb.h"
diff --git a/src/wallet/test/wallet_tests.cpp b/src/wallet/test/wallet_tests.cpp
index 659407c10b65..32397d0d106c 100644
--- a/src/wallet/test/wallet_tests.cpp
+++ b/src/wallet/test/wallet_tests.cpp
@@ -412,6 +412,8 @@ BOOST_FIXTURE_TEST_CASE(importwallet_rescan, TestChain100Setup)
     SetMockTime(KEY_TIME);
     coinbaseTxns.emplace_back(*CreateAndProcessBlock({}, GetScriptForRawPubKey(coinbaseKey.GetPubKey())).vtx[0]);
 
+    std::string backup_file = (SetDataDir("importwallet_rescan") / "wallet.backup").string();
+
     // Import key into wallet and call dumpwallet to create backup file.
     {
         CWallet wallet;
@@ -423,7 +425,7 @@ BOOST_FIXTURE_TEST_CASE(importwallet_rescan, TestChain100Setup)
 
         JSONRPCRequest request;
         request.params.setArray();
-        request.params.push_back((pathTemp / "wallet.backup").string());
+        request.params.push_back(backup_file);
         ::pwalletMain = &wallet;
         ::dumpwallet(request);
     }
@@ -435,7 +437,7 @@ BOOST_FIXTURE_TEST_CASE(importwallet_rescan, TestChain100Setup)
 
         JSONRPCRequest request;
         request.params.setArray();
-        request.params.push_back((pathTemp / "wallet.backup").string());
+        request.params.push_back(backup_file);
         ::pwalletMain = &wallet;
         ::importwallet(request);
 
diff --git a/src/wallet/wallet.cpp b/src/wallet/wallet.cpp
index ef529162553b..c00b6f23fa8e 100644
--- a/src/wallet/wallet.cpp
+++ b/src/wallet/wallet.cpp
@@ -18,7 +18,7 @@
 #include "script/sign.h"
 #include "scheduler.h"
 #include "spork.h"
-#include "util.h"
+#include "util/system.h"
 #include "utilmoneystr.h"
 #include "zpivchain.h"
 
diff --git a/src/wallet/wallet.h b/src/wallet/wallet.h
index 27c225ad9ea0..ae19ef76ac38 100644
--- a/src/wallet/wallet.h
+++ b/src/wallet/wallet.h
@@ -24,7 +24,7 @@
 #include "primitives/transaction.h"
 #include "sapling/address.h"
 #include "guiinterface.h"
-#include "util.h"
+#include "util/system.h"
 #include "util/memory.h"
 #include "utilstrencodings.h"
 #include "validationinterface.h"
diff --git a/src/wallet/walletdb.cpp b/src/wallet/walletdb.cpp
index dda03280b919..0e7b50007caf 100644
--- a/src/wallet/walletdb.cpp
+++ b/src/wallet/walletdb.cpp
@@ -15,7 +15,7 @@
 #include "sapling/key_io_sapling.h"
 #include "serialize.h"
 #include "sync.h"
-#include "util.h"
+#include "util/system.h"
 #include "utiltime.h"
 #include "wallet/wallet.h"
 
diff --git a/src/warnings.cpp b/src/warnings.cpp
index 9be652d5c53c..a7b607a48e44 100644
--- a/src/warnings.cpp
+++ b/src/warnings.cpp
@@ -7,7 +7,7 @@
 
 #include "sync.h"
 #include "clientversion.h"
-#include "util.h"
+#include "util/system.h"
 
 RecursiveMutex cs_warnings;
 std::string strMiscWarning;
diff --git a/src/zmq/zmqabstractnotifier.cpp b/src/zmq/zmqabstractnotifier.cpp
index 53dac44aebc8..d39d0be0fd7d 100644
--- a/src/zmq/zmqabstractnotifier.cpp
+++ b/src/zmq/zmqabstractnotifier.cpp
@@ -3,7 +3,7 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include "zmqabstractnotifier.h"
-#include "util.h"
+#include "util/system.h"
 
 
 CZMQAbstractNotifier::~CZMQAbstractNotifier()
diff --git a/src/zmq/zmqnotificationinterface.cpp b/src/zmq/zmqnotificationinterface.cpp
index 110e2df44ba4..18dfe917bbe9 100644
--- a/src/zmq/zmqnotificationinterface.cpp
+++ b/src/zmq/zmqnotificationinterface.cpp
@@ -7,7 +7,7 @@
 
 #include "version.h"
 #include "streams.h"
-#include "util.h"
+#include "util/system.h"
 
 void zmqError(const char *str)
 {
diff --git a/src/zmq/zmqpublishnotifier.cpp b/src/zmq/zmqpublishnotifier.cpp
index ee08858fe18e..67998ee27f96 100644
--- a/src/zmq/zmqpublishnotifier.cpp
+++ b/src/zmq/zmqpublishnotifier.cpp
@@ -5,7 +5,7 @@
 #include "zmqpublishnotifier.h"
 
 #include "chainparams.h"
-#include "util.h"
+#include "util/system.h"
 #include "crypto/common.h"
 #include "validation.h"     // cs_main
 
diff --git a/src/zpiv/mintpool.cpp b/src/zpiv/mintpool.cpp
index 775f056919dc..16c8f39b6051 100644
--- a/src/zpiv/mintpool.cpp
+++ b/src/zpiv/mintpool.cpp
@@ -3,7 +3,7 @@
 // file COPYING or http://www.opensource.org/licenses/mit-license.php.
 
 #include "mintpool.h"
-#include "util.h"
+#include "util/system.h"
 
 
 CMintPool::CMintPool()