Re: rebuild raid6 after two failures

[NeilBrown <neilb@suse.de>]

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On Tue, 31 Jan 2012 20:42:28 -0800 Keith Keller
<kkeller@wombat.san-francisco.ca.us> wrote:

> On 2012-01-31, Keith Keller <kkeller@wombat.san-francisco.ca.us> wrote:
> >
> > I recently had a RAID6 lose two drives in quick succession, with one
> > spare already in place.  The rebuild started fine with the spare, but
> > now that I've replaced the failed disks, should I expect the current
> > rebuild to finish, then rebuild on another spare?
> 
> [snip]
> 
> Well, for better or worse, this is now a moot question--I had another
> drive kicked out of the array, I believe prematurely by the controller.
> I was able to --assemble --force the array, and it is now rebuilding
> two spares instead of one.  AFAIR there was no activity on the
> filesystem at the time, so I am optimistic that the filesystem should be
> fine after an fsck.  Thanks to the advice from last time which suggested
> --assemble --force instead of --assume-clean in this situation.
> 
> Could it have been the older version of mdadm that didn't tell the
> kernel to start rebuilding the added spare?  I have made 3.2.3 my
> default mdadm, which I hope alleviates some of the issues I've had with
> rebuilds not starting.  (As an aside, I've also bitten the bullet and
> decided to swap out all the WD-EARS drives for real RAID drives; ideally
> I'd replace the controller, but I don't want to invest the time needed
> to replace and test all the components properly.)

If a spare is being rebuild when another spare is added, it keeps with the
first rebuild rather than restarting from the beginning.

This means that you get some redundancy sooner, which is probably a good
thing.

NeilBrown

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