Backup verification on zfs

[Einar Stenberg]

Hi,

I'm seeing that verification jobs are taking up quite a bit of time on the backup server. (I am using the only verify new snapshots thing)

And then i realized, is checksumming and checkimg for bitrot not what zfs scrub jobs are doing?

Is it then even neccesary to run verify if the backing filesystem is on zfs?

 

[fabian]

verify does both a logical consistency check (are all chunks referenced in a backup snapshot available on disk?) and a bit-rot check (are the referenced chunks correct?). the latter part is also handled by ZFS, albeit on a different level.

 

[Einar Stenberg]

verify does both a logical consistency check (are all chunks referenced in a backup snapshot available on disk?) and a bit-rot check (are the referenced chunks correct?). the latter part is also handled by ZFS, albeit on a different level.

Would it then make sense to have a verification mode for zfs, that is "light"?
Ie. It only checks the logical consistency?

 

[fabian]

we've thought about, but haven't implemented such a mechanism yet (it's better to only have a strong verify that does the full work, than users confusing a light verify for one that does the whole thing and then being surprised about bit-rot not being detected).

note that garbage collection also iterates over all snapshots and checks whether each chunk exists, although it doesn't display that information in a very nice fashion yet it also serves as a sort of consistency check without the "digest verification". so as long as you run GC regularly, you should get informed about any chunks that are still referenced which went missing.