rsync rewrites all blocks of large files although it uses delta transfer

Kevin Korb kmk at
Wed Feb 13 22:32:14 UTC 2019

It can't do what you want.  The closest thing would be --compare-dest.

On 2/13/19 5:26 PM, Delian Krustev wrote:
> On Wednesday, February 13, 2019 11:29:44 AM EET Kevin Korb via rsync 
> <rsync at> wrote:
>> With --backup in order to end up with 2 files it has to write out a
>> whole new file.
>> Sure, it only sent the differences (normally that means
>> over the network but there is no network here) but the writing end was
>> told to duplicate the file being updated before updating it.
> The copy is needed for the comparison of the blocks as "--inplace" overwrites 
> the destination file. I've tried without "--backup" but then the delta 
> transfers too much data - close to the size of the backed-up files.
> The copy is in a temp file system which is discarded after the backup (by "rm 
> -rf"). This temp filesystem is not log structured or copy-on-write so having a 
> copy there is not a big problem. Although I don't want a backup of all files 
> which are modified but rather a TMPDIR.
> The ideal workflow would be to compare SRC and DST and write changed blocks to 
> the TMPDIR, then read them from TMPDIR and apply it to DST.
> Cheers
> --
> Delian

	Kevin Korb			Phone:    (407) 252-6853
	Systems Administrator		Internet:
	FutureQuest, Inc.		Kevin at  (work)
	Orlando, Florida		kmk at (personal)
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