ZFS behavior when device disappears

Pawel Jakub Dawidek pjd at FreeBSD.org
Tue Apr 20 06:40:12 UTC 2010

On Tue, Apr 13, 2010 at 05:39:30PM -0600, Jason J. W. Williams wrote:
> Hello,
> Currently, we're an OpenSolaris shop but with the way things are going
> over at Oracle/Sun we're starting to evaluate our options for keeping
> ZFS but moving off Solaris. One of my concerns is that FreeBSD is
> implementing ZFSv14 (ZFS itself is up to v23 I believe). For quite a
> long time, ZFS under Solaris had a real problem with the following
> scenario:
> * Hard drive starts to die
> * Controller and SCSI subsystem continue to retry an I/O rather than
> failing fast
> * Even if the I/O does fail fast ZFS doesn't really notice a spike in
> I/O failures and continues to use the drive.
> * Result: I/O on the zpool stalls completely while the I/Os continue
> to be tried against the drive.
> This got fixed in later revs of OpenSolaris by enhancements to ZFS and
> greater integration with the Fault Management Architecture (FMA) of
> Solaris...lots of I/Os failing on a drive get communicated to ZFS who
> then offlines the drive out of the pool.
> My question is, what is the situation in FreeBSD 8 with ZFS if that
> type of situation occurs?

I believe FreeBSD does whatever OpenSolaris did for this version of ZFS.
There is nogoing work to bring v24 to FreeBSD. Basic functionality works
already, but a lot work is still needed. At some point I'll see what we
can do about it, because we don't have FMA in FreeBSD and we would need
to find another way to deal with it. I've limited time I can spend on
ZFS right now, so I'm making small steps, but I'm making good progress

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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