Re: zfs backup question

>> On Fri 19 Jun 2026 at 05:00:31 (-0400), Julien Cigar wrote:

> Is there a way to handle this without having to send the whole dataset
> when backuping?

It might be easiest to compare hashes of the old and new files to create
your backup.  I made two directories with some HTML files: b-old (old
backup) and b-new (production, which will become your current backup).

    me% ls -lF
    drwxr-xr-x 2 vogelke wheel 3264 19-Jun-2026 06:56:12 b-new/
    drwxr-xr-x 2 vogelke wheel 3264 19-Jun-2026 07:01:03 b-old/

I copied b-old to b-new and made some minor changes to b-new:

    * removed b-new/1.htm
    * added b-new/2.htm
    * changed b-new/3.htm

I hashed the files, sorted by filename and compared:

    me% cd b-new
    me% md5sum * | sort -k2,2 > ../b-new.sum
    me% cd ../b-old
    me% md5sum * | sort -k2,2 > ../b-old.sum
    me% cd ..

    me% diff b-old.sum b-new.sum
    41a42
    > 8f9ea97ad8024ff88c1b39a518e51838  2.htm
    43c44
    < eeaf2f41b27f5fe6cffc6342d016ff84  3.htm
    ---
    > 6c807fc0929464b31b432563bfce5be0  3.htm
    45d45
    < 0e3876813506bf815a76d60adb1fe8db  1.htm

You can copy your old backup and update these files when creating your
current backup; the deleted files simply won't exist.  If you're also
creating directories, that would be more complicated.  I don't know if
you can run something like "syncthing" between two existing directories
in their own jails.

-- 
Karl Vogel                      I don't speak for anyone but myself

The server room doubled as the marketing dept's wine cellar.
I no longer work there.     --Reddit "janky setup" comment, 6 Jun 2026