Does UFS2 send BIO_FLUSH to GEOM when update metadata (with softupdates)?

[Pawel Jakub Dawidek]

On Wed, Nov 23, 2011 at 09:44:44PM +0200, Kostik Belousov wrote:
> On Wed, Nov 23, 2011 at 11:00:26PM +0400, Lev Serebryakov wrote:
> > Hello, Freebsd-fs.
> > 
> >   Does UFS2 with softupdates (without journal) issues BIO_FLUSH to
> > GEOM layer when it need to ensure consistency on on-disk metadata?
> No. Softupdates do not need flushes.

Well, they do for two reasons:
1. To properly handle sync operations (fsync(2), O_SYNC).
2. To maintain consistent on-disk structures.

The second point is there, because BIO_FLUSH is the only way to avoid
reordering (apart from turning off disk write cache).

SU assumes no I/O reordering will happen, which is very weak assumption.

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