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+# backup
+A simple, but cross-platform and efficient backup program
+
+This module implements a backup procedure, with optimisations
+for NTFS drives.
+Source can be any directory, for example C:/
+Target is a directory, with each backup getting a subdirectory within it.
+For example, C:/snapshots/20101103.
+The target is essentially a copy of the source, except that:
+  - some files and/or directories may have been excluded, and
+  - files and/or directories that have not changed since the previous
+    backup will be links (hard for file, sym for dirs to the copies
+    in the previous backup dir).
+Some state files are maintained in the base target dir:
+  - journal for the state of the NTFS journal from the last
+  backup, including a dir map.
+  - previous for the previous successful backup name
+  - exclusions is a list of files and dirs to exclude from backups.
+Basic algorithm:
+  - Input is source directory, target directory, and name.
+  - Read exclusions file and journal file.
+  - Open journal and build list of changed paths.
+  - Iterate over source, using changed paths to optimise if possible.
+     - For each file/dir, either copy in or make link to copy in previous
+       backup.
+  - Save journal file.
+  
+Example:
+backup.py C:/ C:/snapshots 20101103