Re: saving RAIDframe parity accross a panic

[der Mouse <mouse%Rodents-Montreal.ORG@localhost>]

>> Another RAIDframe question: Is there a decent way to replace a
>> component on the fly that one is afraid of failing?
>> Of course, I can add a hot spare, fail that component and begin a
>> reconstruction.  But then I have a three-hour window where, if
>> another component fails, I have shot myself in the foot.
> Can you schedule downtime of the RAID sets for those 3 hours?  If you
> can't, then you're rather stuck with that 3-hour window of
> vulnerability.

There actually is a way around this, but it requires preparation at
RAID setup time.

What you do is, instead of building your RAID 5 out of disk partitions,
make each disk partition a member of a two-component RAID 1 (mirror)
set, with the other member missing.  Then build your RAID 5 atop the
RAID 1s.

Then, if you want to swap out a disk underneath the RAID 5, you hot-add
the new disk to the relevant underlying RAID 1, wait until the RAID 1's
reconstruct is done, and pull the original.  The RAID 5 never knows
anything is happening.  Mark the RAID 1s autoconfiguring and you don't
even have to think about updating their config files.

However, as I said above, this requires that it be designed in from the
beginning.  Not much help in your current predicament, unless you can
take the whole thing out of service for a future-proofing rebuild.

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