ZFS behavior when device disappears

[Jason J. W. Williams]

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?

Thank you in advance for your help.

-J