On Wed, Dec 30, 2015 at 10:40 AM, gregrwm
<[email protected]> wrote:
> during a full backup (whether using checksum-seed or not) if file attributes
> are unchanged but file content no longer matches, what happens? does
> backuppc merely treat it as a changed file, or does it treat this as an
> inconsistent situation worthy of admin attention?
It is just a changed file.
> is something written to a
> log? which log and what is written (so i can grep)? and/or is it reported
> via email?
>
> does checksum-seed merely make use of the same backuppc signature hash
> already used for pooling, or does it compute a different checksum? either
> way, it ought to usually or sometimes be possible to see whether bit rot
> occurred in the original or the backup (eg does the original or the
> backuppc_zcat still match the checksum). does backuppc look for this and
> report accordingly?
With checksum-seed enabled, on the 2nd full backup of an unchanged
file the block checksums used by rsync are cached on the server side
by appending them to the pooled file.
> also please let me know if i understand this correctly: during incremental
> backups, if file attributes have not changed it is presumed the file content
> also has not changed.
Yes, that is correct.
> during full backups, if checksum-seed remains
> commented, then for every file the entire content is compared via hash for
> every block, or if checksum-seed is enabled, then only
> ~RsyncCsumCacheVerifyProb of files will have their entire content checked
> (via hash for every block), while all other files will have their backuppc
> signature checksum computed and merely that will be compared. have i got
> that right? is there a good place other than the source to read about how
> this works in any particular release/version?
On the 2nd full, the server-side copy is read (and uncompressed) to
compute the block checksums for the comparison. After that, the
cached values will be used except for the RsyncCsumCacheVerifyProb
percentage. The files are always read on the client side during
fulls, though.
--
Les Mikesell
[email protected]
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