--dry-run reliability ?

daitheflu at free.fr daitheflu at free.fr
Fri Jun 13 15:14:16 MDT 2014


I'm using rsync to backup my files. I have also added a pre-backup step where the script checks if there is enough space on the destination for rsync to run successfully. The goal is to make room (delete oldest backups) if that's not the case.

I'm running rsync with -ahAXS --numeric-ids --link-dest options.

For my pre-backup step, I'm currently using the same options + --dry-run --no-h --stats. I then parse the "Total transferred file size" line, add a 20% (!) padding and compare the result with the result of a "df" call on destination.

It seemd to work properly until I decided to add some ACL on the source device.
I didn't really know how rsync would handle the situation, but understood that it may have to backup all the files (instead of hardlinking them) because of this change.

The dry run reported that it would need about 1400 MB and I have around 30 000 MB of free space, so it should have ran properly. Sadly, I got the "no space left on device" error.

So, is it safe to rely on the stats provided by a dry run to achieve my goal ?
Does the --dry-run option take care of ACL/permissions changes ?

Thanks a lot for your work and help, rsync is really a wonderful tool.



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