[kwlug-disc] question about use of rsync --checksum flag

[Erik Schnetter]

The `--checksum` flag of rsync isn't meant to detect errors on the
receiver side. Rather, this is a more reliable mechanism to see
whether the remote file differs from the local file. By default, rsync
only checks the file size and the file's modification time, and if
they agree, rsync assumes the files are the same. In principle this
can fail, in particular if one plays shenanigans with the file
modification time.

In other words, this calculates a checksum BEFORE transferring a file,
not afterwards to check whether the transfer worked correctly.

-erik

On Sun, Jun 9, 2024 at 4:27 PM Mikalai Birukou <mb at 3nsoft.com> wrote:
>
> I always hear "Do you test your backups?" reminder.
>
> zpool(s) scrub themselves. It feels like testing, at least on a storage
> layer.
>
> But what about those rsync powered places without zpool? Is checksum-ing
> useful? Are there any strategies?
>
> Or, if both source and destination are not zfs-level reliable, does
> checksum-ing make sense if it can introduce errors into backups?
>
>
>
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-- 
Erik Schnetter <schnetter at gmail.com>
http://www.perimeterinstitute.ca/personal/eschnetter/