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Date: Sun, 21 Jun 2015 16:49:46 -0400
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To: Willem Jan Withagen <wjw@digiware.nl>
CC: fs@freebsd.org
Subject: Re: This diskfailure should not panic a system, but just disconnect
 disk from ZFS
References: <5585767B.4000206@digiware.nl>
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Also:

> And thus I'd would have expected that ZFS would disconnect /dev/da0 and
> then switch to DEGRADED state and continue, letting the operator fix the
> broken disk.

> Next question to answer is why this WD RED on:

> got hung, and nothing for this shows in SMART....

You have a raidz2, which means THREE disks need to go down before the 
pool is unwritable. The problem is most likely your controller or power 
supply, not your disks.

Also2: don't rely too much on SMART for determining drive health. Google 
released a paper a few years ago revealing that half of all drives die 
without reporting SMART errors.

http://research.google.com/archive/disk_failures.pdf