Re: Adding hot spare using a disk from an existing RAID 5 string

We have been around the universe on this one and decided to bail.

In our case we had 18 drives in a RAID-6 set on a Power 6 with 2 hot spares.

The drives are SCSI and we discovered that the hardware does NOT support
hot spares in all disk positions so as we lost drives and they were
replaced by hot spares we ended up in a situation where the open drive
slots would not support hot spares.

We thought the solution was to remove the two drives from the ASP and then
remove them from the RAID-6 set in DST.

We discovered that there was a point where we would have "broken" the RAID
set and we would have lost protection. Further we discovered that the
time to rebuild the RAID set was anywhere from "three to a hundred hours"
(direct quote from IBM Rochester).

We decided that the risk was not commensurate with the gain and decided to
just stick with 18 drives in the RAID-6 set where we can lose up to two
drives simultaneously without disaster.

In the meantime we have two drives on the shelf ("manual spares") ready to
go should we lose a drive.

So, in the end it wasn't worth the trouble. We'll wait until we upgrade
to Power 8 or 9 and get external storage or SAS.


Jerry

OS's version is 7.2 and the machine is an 8202-E4D. The controller is a
2B4C and there are 8 19A1 disks in a RAID5 string.

The customer want to use one of the disks (occupation is around 39%) as an
hot spare.

The suggeste procedure is:

- remove a disk from the raid array
- format the disk
- start hot spare

Is that correct?

The procedure "Removing disk units that have device parity protection from
a disk pool without mirrored protection" in Disk management list some
steps:
...
4 - Restart your system and select the option to use dedicated service
tools (DST).
5 - Remove disk units that you plan to remove from the system.
6 - Exclude the disk units from device parity protection. If you were
successful in excluding the disk units, skip to task 8. Otherwise,
continue
to task 7.
7 - Stop device parity protection for all the disk units in the
Input/Output Processor (IOP).
8 - Physically remove disk units. If you stopped device parity protection
in task 7, continue with task 9. If you did not stop device parity
protection, skip to task 10.
9 - Start device parity protection again.
10- Verify that your disk unit configuration is correct.
...

I'm not confortable with point 6 (Otherwise, continue to task 7). "Stop
device parity" is that a common situation?


Thanks in advance for you suggestions / comments
--
Marco Facchinetti

Mr S.r.l.

Tel. 035 962885
Cel. 393 9620498

Skype: facchinettimarco
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