about rsyncing of block devices

[Stephane Chazelas]

2010-06-15 18:10:07 +0200, Václav Ovsík:
[...]
> I already wrote a patch, but without response there.
> http://lists.samba.org/archive/rsync/2010-January/024538.html
> 
> Oh yeah, the patch is not in the archive! 8-)
> 
> Ok, including it here now:
[...]

Thanks Zito for sharing.

a lot more complete than mine.

Same problem though. It only allows device files to be
synchronised like other files. So it's gonna be quite slow and
won't necessarily minimise the disk bandwidth, only the network
bandwidth.

And by the way, when doing regular backups, it would be nice to
be able to keep the checksums, so that they don't need to be
computed each time.

I mean, when you do a:

rsync --no-whole-file a b

you compute the checksums of both a and b. After rsync has
completed, a's checsum is b's checksum.

If after a while you redo:
rsync --no-whole-file a b

"a" having been modified and not "b", you'll still recompute
"b"'s checksum even though it hasn't been modified. In the
simple perl-based solution I suggested, it can be implemented
easily (just store the sums away while they're being computed).

Some --dest-check-sum= --src-check-sum= and  --save-check-sum
option to rsync (only applicable when syncing one file to
another, or saving the checksum of every file in a specific
format) could be useful.

Cheers,
Stephane