Re: Hot-swapping disks of different size in a RAID set

Be prepared for a very long RAID build on that size drive... especially
since there will be data on the drives.

On Fri, Jul 15, 2011 at 12:38 PM, John Jones <chianime@xxxxxxxxx> wrote:

DrFranken, so is what you're describing the following:
1. GO SAVE/21
2. End RAID5 *At this point the system has no protection from disk
failures*
3. Disk-by-disk, logically remove each 70GB disk via SST, replace it with a
280GB, and add the 280GB to the ASP
4. Do a load source migration type of trick to move the load source
5. Re-establish RAID5 to gain protection from disk failure
6. Probably do some form of STRASPBAL when done

Re: Item 5: IDK about 525s but on our Power5+ 570 we IPL one V6R1 LPAR from
280GB SCSI disks (4329s on a 2780).

On Fri, Jul 15, 2011 at 1:54 PM, DrFranken <midrange@xxxxxxxxxxxx> wrote:

Yes.  (this is totally crazy)

You will need to take the system down during part of this at least.

1) You cannot use a 140 or 280GB Drive to replace a 70GB drive in a RAID
set. Even if you could (as some vendors allow) it would be treated as a
70GB drive.

2) You cannot replace the Load Source disk unit without an IPL in any

case.

3) Replacing drives in the manner of which you speak can mostly be done
live but YOU ARE EXPOSED during 100% of the swapping. A disk failure
between the beginning of 'STOP RAID' to the completion of 'START RAID'
at the end means *RELOAD. As a consequence a SAVE 21 (maybe 2?) before
you start is mandatory and if the system is running production you still
could lose that.  It can work but not without at least one IPL PER DISK
PULL. (More than one disk could be pulled at a time.)

4) NOte that if you are on V7R1 the disks can be completely removed
without an IPL (except the Load Source.)

5) I do not believe you can IPL from a 280GB Disk unit on a 525. There
was a restriction there and I *think* it's still there for SCSI drives.
So 140 GB units are best choice.

  - Larry 'DrFranken' Bolhuis

On 7/15/2011 2:03 PM, Johnny Lee Lenhart wrote:

Hi there:

We have a 9406-525 with 8 4327 (70 GB) disk drives in a single RAID

set.

The drives are in the system enclosure and there are no additional

slots

available.  We are at 85% DASD utilization.

We have an idea for increasing our DASD capacity without taking our
system down.  Our thought is that we could fail one of the 4327 drives,
replace it with a 4328 (140 GB) or 4329 (280 GB) and let the RAID
controller rebuild it, and that we could do this one-by-one until we
have replaced all of the drives, thus doubling or tripling our current
DASD.

Is this totally crazy?  One person I've talked with suggested that you
can't have mixed sized disks in one RAID array, but our network admin
thinks we did have this in an 810 we used to run.  Someone else thought
that we might have issues increasing our DASD capacity without
increasing disk arms, but our current performance metrics don't seem to
support that concern.  At any rate, we are willing to take that risk.
Our main interest right now is answering the question about whether or
not this disk-at-a-time replacement into the same RAID array is
possible.  We really can't afford to have our system down for the time
it would take to do the backup/change disks/restore method.

Thoughts?

Thanks,

                                             Johnny Lee Lenhart
                                             Sr. Technical Specialist
                                             Brattleboro Memorial
Hospital
                                             Brattleboro, Vermont  USA


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