Migration from the KQ Implementation

Gordan Bobic gordan.bobic at gmail.com
Wed May 4 21:08:44 EDT 2011


On 05/05/2011 02:05, Jason J. W. Williams wrote:
>> Backups are of paramount importance, sure, but fsck is important, too,
>> especially when a fsck pass might take 10 minutes vs. 2 days for restoring
>> all the data from a backup (and the inevitable loss of anything since the
>> last backup.
> The question is what are expecting a ZFS fsck to do? Rollback to an
> earlier consistent form of the filesystem? By default ZFS attempts
> that already.

No, that's just basic journal recovery and no fsck is needed. ext[3,4] 
does that, and there is still fsck for when that just isn't sufficient.

> For situations where the hardware controller outright
> lies to the OS about what it's doing and causes corruption, PSARC
> 2009/479 (aka zpool recovery) attempts to clear out as many bad
> transaction groups as it can to return the pool to a consistent
> mountable state.

You are still only talking about missing commits. I'm talking about 
different scenarios that aren't based on just the recent data getting 
trashed.

> So that's really question...beyond those things what
> would a ZFS fsck do that wouldn't require a custom recovery job?

The same things that ext3 fsck does when the journal doesn't ensure a 
clean fs.

Gordan



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