ZFS behavior when device disappears

Jason J. W. Williams jasonjwwilliams at gmail.com
Tue Apr 20 13:24:56 UTC 2010

Hi Pawel,

Thank you very much for the response! Please forgive some of my
questions, as I'm a bit unfamiliar with the FreeBSD port.

What is the nature of the port? Is it something where each new version
of ZFS is a from-scratch effort to some degree? Or is it a point where
new ZFS versions are a matter of just making the newer features


On Tue, Apr 20, 2010 at 12:40 AM, Pawel Jakub Dawidek <pjd at freebsd.org> wrote:
> 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
> too.
> --
> 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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