[Disk Balance] How to balance tablet among disks in some BE. #4476
Description
Is your feature request related to a problem? Please describe.
The current balancing strategy is only used for data balancing between different BEs. But it cannot handle the data balance between different disks on the same BE. We often find that the usage of different disks on a BE varies greatly.
#4373 try to use "two random choices algorithm to try to choose a more reasonable disk.
But for existing data, we need a way to migrate and balance data between disks.
Describe the solution you'd like
We can use storage medium migration task to perform tablet migration.
This is a simple and feasible solution. We can try to support this way first.
But this way needs to lock the tablet during migration to prevent operations such as writing.
So it is a feasible but not elegant solution. We can try to implement this function in a similar way
to schema change in the future.