ZFS - hot spares : automatic or not?

Dan Langille dan at langille.org
Thu Jan 20 02:40:18 UTC 2011

On 1/11/2011 11:10 AM, John Hawkes-Reed wrote:
> On 11/01/2011 03:38, Dan Langille wrote:
>> On 1/4/2011 11:52 AM, John Hawkes-Reed wrote:
>>> On 04/01/2011 03:08, Dan Langille wrote:
>>>> Hello folks,
>>>> I'm trying to discover if ZFS under FreeBSD will automatically pull
>>>> in a
>>>> hot spare if one is required.
>>>> This raised the issue back in March 2010, and refers to a PR opened in
>>>> May 2009
>>>> * http://lists.freebsd.org/pipermail/freebsd-fs/2010-March/007943.html
>>>> * http://www.freebsd.org/cgi/query-pr.cgi?pr=134491
>>>> In turn, the PR refers to this March 2010 post referring to using devd
>>>> to accomplish this task.
>>>> http://lists.freebsd.org/pipermail/freebsd-stable/2010-March/055686.html
>>>> Does the above represent the the current state?
>>>> I ask because I just ordered two more HDD to use as spares. Whether
>>>> they
>>>> sit on the shelf or in the box is open to discussion.
>>> As far as our testing could discover, it's not automatic.
>>> I wrote some Ugly Perl that's called by devd when it spots a drive-fail
>>> event, which seemed to DTRT when simulating a failure by pulling a
>>> drive.
>> Without such a script, what is the value in creating hot spares?
> We went through that loop in the office.
> We're used to the way the Netapps work here, where often one's first
> notice of a failed disk is a visit from the courier with a replacement.
> (I'm only half joking)
> In the end, writing enough perl to swap in the spare disk made much more
> sense than paging the relevant admin on disk-fail and expecting them to
> be able to type straight at 4AM.
> Our thinking is that having a hot spare allows us to do the physical
> disk-swap in office hours, rather than (for instance) running in a
> degraded state over a long weekend.
> If it's of interest, I'll see if I can share the code.

I think this very much of interest.  :)

Dan Langille - http://langille.org/

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