On Mon, Sep 17, 2012 at 12:58:28PM -0400, Timothy J Massey wrote:
> Les Mikesell <lesmikes...@gmail.com> wrote on 09/17/2012 11:01:25 AM:
> > On the 2nd it will read/uncompress
> > everything for block-checksum verification. If you have enabled
> > checksum caching, fulls after the 2nd will not have to read/uncompress
> > unchanged files on the server side.
>
> I'm going to have to test this... but I really don't like the fact that
> with checksum caching a file corrupted on the backup server will remain
> undetected--until the user tells me so when I restore it... :(
AFAIK this is not correct. If checksum caching is enabled, backuppc
will check the cached checksums against the actual file contents based
on the setting of the:
$Conf{RsyncCsumCacheVerifyProb} = 0.10;
variable. So in my case it would take about 10 days to verify the
pool. Granted this is a probabilistic ratio, and I haven't looked at
the code to make sure that this means:
every file in the pool would be checked every 10 days
only files that exist on the end clients are checked every 10 days
some files may be checked every day in 10 days and some files
won't be checked
but this addresses the issue you brought up.
Also even with checksums turned off, you could have an older copy of
the file in the pool go bad and you wouldn't know it till you tried to
restore it, so having checksum off doesn't protect you from bad data
in the pool except for the most recently used files.
(We also won't discuss having corruption in putting the current bits
on disks that trashes the curent backup copy. Which frankly there is
very little short of zfs/btrfs type filesystem that can provide some
measure of protection/detection.)
--
-- rouilj
John Rouillard System Administrator
Renesys Corporation 603-244-9084 (cell) 603-643-9300 x 111
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