vgcreate array clariion CX 500. Do I need 4 pv?

[isaac_loven]

Hi Fourmers,
I want to assign LUNS from our new CX500 to our new RP4440.
I know HP recomended for their VA7400 array using 4 LUNS per VG. The reason was something to do with multiple scsii queues.
Should I do this with the CX500?
Thanks.
Isaac

[Iain Ashley]

Hi Isaac,
Simply put, the more luns you can stripe across in LVM the better performance you will get. Obviously this is limited by the available bandwidth etc, so you will reach a plateu at some point. Where this happens depends a lot on your system's confiuration. Virtualised storage also complicates this. Generally 4 Luns is a good compromise between complexity and performance, but if you can afford the time you could do your own testing to get the optimal mark. Remember though, to get the benefit, you must stripe your luns:

lvcreate -i -s

Where number of stripes is the number of luns you want to stripe across. Talk to your apps guys to get the optimal stripe size, this will be the app's default write size.

Regards
Iain Ashley