Remove disks from 12H?

[Greg Stark_1]

We recently added 4 disks to our 12h. We left the disks unallocated to try and increase performance by increasing the amount of unallocated disk space. We would like to now remove 2 of these and check performance again.

I just wanted to confirm that we can remove these drives one at a time without any prep work or problems. I think we just remove 1, wait for the 12h to show "ready" again, then remove another... and so on. Is this right?

Thanks,
Greg

[harry d brown jr · Accepted solution]

Greg,

You must be looking for "point of diminishing returns", otherwise I'd suggest just fully populating the 12H. Hopefully you have two controllers and are using both IO paths (alternating).

We'd be interested in your results, so please remember to post back.

live free or die
harry

[Helen French]

Hi,

If i understood your question correctly, then the answer is, it depends on your RAID level. If you are using RAID 5, then it needs a minimum of 3 disks in the LUN and therefore you cannot remove 2 out of 4. IF it's RAID 1, then you can remove the disks, as you keep the mirror disk.

See this site for manuals of AutoRaid 12H:

http://www.hp.com/cposupport/manindex/hpsurestor19162_eng_man.html

HTH,
Shiju

[A. Clay Stephenson]

Hi Greg:

You can remove the disk but I suggest that you have 'Active Hot Spare' enabled and 'Auto Rebuild' enabled. Then remove one drive at a time and wait for the light show to finish - which can take quite a while.

I can tell you that the biggest 'hinge' point occurs typically at 8 drives; the improvements are still noticable at 10; and slight going to 12 drives. It is also a function of the amount of unallocated space; i.e. that which is not configured as a LUN. Whenever possible I try not to exceed about 55% capacity and I also make sure that the I/O is split across both external SCSI paths. I find that there is no advantage to exceeding more than 2 LUN's per VG. My favorite way is to create 2 equally sized LUN's per VG. LunA should be primary SCSI path X, secondary Y. LunB should be primary SCSI path Y, secondary X. You then stripe each LVOL in this VG across both LUNS.
If you are using vxfs filesystems, 64k stripe size seems to perform best.

Regards, Clay

[Vincent Farrugia]

Hi,

Yes, remove ONE AT A TIME, taking care to wait until the machine rebuilds the data, then remove the next.

Vince