Re: definiing deduplication

[Stefan Monnier <monnier@iro.umontreal.ca>]

>> Arguably this can be considered as a bug in the application (because
>> a failure in the middle could thus result in an inconsistent state).
> A backup programmer or operator does not necessarily have influence on
> such applications.

Indeed it remains a real problem, that can be solved only with
bug reports and patches.

>> if you don't use snapshots, [...] the bug is in the backup
>> process itself.
> The backuper is not to blame if the backupee filesystem cannot make
> snapshots, and anyways snapshots don't completely solve the consistency
> problem of backups.

Presumably the "backuper" is the sysadmin, i.e. the same (group of)
person who chose the filesystem, so I'd say yes the "backuper" is
to blame.

BTW, I can't think of any filesystem that can't do snapshots.  E.g. I use
snapshots with ext4: just ask your block layer to do the snapshot rather
than your filesystem (in my case I use LVM snapshots).

> Having multiple backups of the same backupee reduces the risk to have
> no consistent copy when the backup needs to be restored.

Agreed.


        Stefan