Others have already mentioned REPLACEMIRRVOL.
In the last three years or so I've probably
had to use that command 6 - 8 times to put a
mirror pair back together (we have five 9GB
hot-swap drives in each of two Jamaica boxes).
REPLACEMIRRVOL has never failed to resurrect
the mirror pair for us...   If it ever does,
we adopted this method for replacing a hot-
swap mirrored drive:

We keep one spare hot-swap disc module inserted
and spinning in each of our two Jamaica boxes;
in "SCRATCH" status (on balance figure better to
do that, than to leave the spares with the heads
parked and powered down in a cabinet somewhere).
We have the Jamaica chassis itself on hardware
maintenance (for something like only $10 a month;
but do NOT have any of the spindles themselves on
maintenance.

If we ever have a hard failure on a mirrored
spindle, we will just pull out the bad drive and
swap in one of the spare SCRATCH discs.
**************
CAUTION
If you use the above scenario, after you pull
out the first spindle WAIT UNTIL THE JAMAICA
BOX HAS "STABILIZED" AGAIN BEFORE PULLING OUT
THE SECOND SPINDLE:  This may take a minute or
two;  depending on how many spindles you have.
If there is little or no activity on the SCSI
channel, you can usually tell things have
"stabilized" by waiting until the polling of
each spindle has completed (LEDs on each disc
momentarily go on and then stay off).  If you
do NOT wait for the "intermediate stabilization"
to complete, there is a good chance that mirror
disc will get "confused";  and decide that it
needs to resynchronize ALL the mirror volumes;
not just the one that you swapped.  This can
take "a while";  and can have a very noticeable
impact on performance if your system is busy
(been there;  done dat).
**************

If we end up using one of our two hot spares,
we order another one.  The "break-even" between
buying a new spare spindle and having all of the
hot-swap spindles on maintenace was only about 6
- 7 months (depending on current prices for the
ST39173WC spindles from a third-party supplier).
Since we have gone years without a hot-swap
spindle failure, we're way ahead.


Of course the other benefit of keeping hot spare
spindles on site is that instead of waiting hours
if not days for the CE to show up, we can be
safely mirrored again as soon as we swap spindles
and mirrored disc completes the resync of that
one bad volume.  This method even works pretty
well for our MPEXL_SYSTEM_VOLUME_SET:  We have
only LDEV 1 and LDEV2 in our <long_name>;  and
keep it 99.9 percent "HP pure".  While we waste
5GB on LDEV1, we pretty much don't care about
that:  If LDEV1 or LDEV2 blow up, with only the
HP stuff on the <long_name> I can do an INSTALL
from our DLTs in only about 30 minutes after
swapping out the bad spindle.  As with mirrored
spindles, this is a whole lot quicker than
waiting for the CE to arrive on-site...

Ken Sletten

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