gjournal: what is it good for?

[Pawel Jakub Dawidek]

On Mon, Apr 19, 2010 at 09:54:28AM +1000, Andrew Reilly wrote:
> So, I've had quite a bit of yoyo-mode over the last week, caused
> by the journal overflow panic that I reported in the previous
> message, and I've noticed that my gjournalled file systems do
> not (ever) mark themselves clean after the journal is replayed,
> and so still require fsck, which takes just as long as it ever
> did.

When gjournal is in use, fsck is still needed, indeed, but only to fix
one type of inconsistencies: orphaned files. This is something we cannot
do without fsck. Still such fsck should be much, much faster.
There are various optimizations that allow to stop fsck as soon as we
fix last orphaned file. If there are no such files, we won't even scan
single cylinder group. We observed fsck time to drop from 8h to few
seconds, so something must be wrong with your configuration if it
takes as much time as without gjournal. You can still run full fsck on
gjournaled file system, of course, but in regular use, 'fsck_ffs -p'
should perform fast fsck.

-- 
Pawel Jakub Dawidek                       http://www.wheelsystems.com
pjd at FreeBSD.org                           http://www.FreeBSD.org
FreeBSD committer                         Am I Evil? Yes, I Am!
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