topic Re: EVA5000 and Performance in Disk Enclosures

EVA5000 and Performance

Hermanator — Tue, 17 Nov 2009 18:22:04 GMT

Is there a performance gain by seperating out your different size disks into different disk groups?
I understand the benefits of using the same size disks in a diskgroup for Disk Failure Protection reasons, but is there a performance hit by having different size drives within a diskgroup?
Which brings up another question, what about different RPM Drives in the same diskgroup? My older 10k rpm drives are being replaced by 15k rpm drives. I have just been placing them back into the same diskgroup. Thoughts on different RPM speeds within a diskgroup?
Thanks

Re: EVA5000 and Performance

Víctor Cespón — Tue, 17 Nov 2009 19:20:08 GMT

If a disk group has disks of different sizes, the bigger disks will contain more data so on average they will have to perform more I/O operations. This can lead to these drives saturating before the others.

Mixing 10K and 15 drives on a disk group has a similar effect, the 15K drives will do their I/O operations faster, the 10K drives will take a little longer. As the data is distributed among all drives, the slower or bussiest ones influence the maximum IOPS that the disk group can do.

Re: EVA5000 and Performance

Hermanator — Tue, 17 Nov 2009 19:44:51 GMT

Vcespon, thank you for your response. There is not a lot I can do about the dfferent RPM Drives that I can think of. As our 10k RPM Drives go bad, they get replaced with 15k RPM drives, so I have no choice but to put them back into the same diskgroup. I guess I could wait until I get 8 bad ones and create a 15k rpm diskgroup with the 8, that could take awhile, but then that also takes away spindles from my original diskgroup.

Hmmm?

Re: EVA5000 and Performance

Uwe Zessin — Tue, 17 Nov 2009 20:12:34 GMT

Think about it in a positive way:

if you replace a 10k RPM disk drive with a 15k RPM one of the same size: the new disk processes I/Os faster, but it does not slow down the whole disk group. The more disks you replace, the faster I/Os get.

Don't understand me wrong:
I don't wish you many bad disk drives ;-)

Re: EVA5000 and Performance

Víctor Cespón — Tue, 17 Nov 2009 23:04:41 GMT

Don't create a small disk group.
It's better to have 20x10K + 10x15K for example, on a single disk group.