Re: Odd behaviour of two identical ZFS servers mirroring via rsync

On Sun, 13 Nov 2022, Mark Saad wrote:
>>
> Bob are you saying when the target is zfs --inplace --no-whole-file helps
> or just in general when you have
> large files ?  Also have you tried using --delete-during / --delete-after  ?

The '-inplace --no-whole-file' updates the file blocks if they have 
changed (comparing the orgin blocks with the existing mirror blocks) 
rather than creating a new copy of the file and moving it into place 
when it is complete.  ZFS does not check if data content has been 
changed while it is being written so a write of the same data will 
result in a fresh allocation based on its Copy On Write ("COW") 
design.  Writing a whole new file obviously significantly increases 
the number of blocks which are written.  Requesting that rsync only 
write to the file for the blocks which have changed reduces the total 
number of blocks which get written.

The above helps quite a lot when using snapshots since then fewer 
blocks are in the snapshots.

I have never tried --delete-during so I can't comment on that.

Bob
-- 
Bob Friesenhahn
bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer,    http://www.GraphicsMagick.org/
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