Optimal LUN size

[Pedro Cirne]

Hi,

I've Symmetrix DMX-2000 and need to present 1 Tera of storage to a HP-UX 11iv3 server with 2 HBA.

Is it better to configure 100 LUN with 10Gb or 10 LUN with 100Gb to have the best performance?

Thks,

[A. Clay Stephenson · Accepted solution]

I think I would beat someone with a baseball bat if they wanted a 1TiB VG comprised of 100 LUN's (which means I would need 200 paths if I use primary and alternate paths).

I think that you are going to find that the differences in performance of 10 X 100GiB or 100 x 10GiB to be negligible while the differences in maintenance will be very significant. In fact, you may very well find that 2 X 500GiB will be quite good.

Bear in mind, that from the standpoint of the host computer, you job is to throw data at the array as fast as you can. What it does with that data is up to it. The array is cache-centric so that the actual disk layout is much less critical. You would probably need to bump up the scsi_max_qdepth -- especially if fewer LUN's are used.

If anything, I might consider increasing to 4 HBA's in which case 4 x 250GiB would be a reasonable layout.

You also don't mention whether or not you are using PowerPath.

The downside to using fewer LUN's is that from the standpoint of host-based performance tools like Glance, you will APPEAR to have disk bottlenecks. Glance doesn't have a clue that this "disk" that is so busy is actually comprised of 10 physical disks with tons of cache in between.

[Hein van den Heuvel]

Neither.
Think towards 5 * 200GB
Immediate performance is the smallest of your concerns.
Think about keeping management simple.
Let the controller do it's thing like caching and striping. That's it only goal in life. Give it a clear picture of what's happening such that it can adapt.
Think about the backup process to be used
Think about fragmentation/defragmentation issues.
Think about being able to 'mv' files without actually copying block around.
Think about not having to 'mv' file to make more space on some storage unit
Think about the controller (DMX) per-lun performance options
Think about not even being able to buy a drive less than 100GB for your home computer.
Think about raid requirements.
and after all that, if there are options left still, then think about performance from the hpux point of view once again

:-)

Hope this helps some,
Hein van den Heuvel (at gmail dot com)
HvdH Performance Consulting

[Pedro Cirne]

Hi,

Thank you, I agree with you and my opinion is the same, I just want to have a second opinion on this subject from other experts!

Thks!