Getting poor write performance on HP P2000 SAN connected to HP Proliant G8 servers

[Dazza76]

I've recently configured some HP DL380 G8s with HP 81Q HBAs connected to a new HP P2000 SAN with 8GB FC connections and am experiencing much slower writes than compared to locally attached disks.  I was expecting a slight performance drop but I'm seeing about a quarter of the speed of locally attached disks.

The setup is 2 x HP DL380 G8s connected to HP 8/8 SAN Switch (Brocade 300) which is then connected to all ports on the SAN.  Both servers have 2 x HP 81Q (Emulex) cards installed each connected to a different switch.  I saw the same performance issues without the switches in place.

I'm using ATTO Bench32 to do the performance comparisons and am seeing write speeds of 1.3GB/s on the local disk compared to less than 400MB/sec on the SAN.

I've checked the write caching on the volumes on the SAN and they're set to write-back (I was hoping this was where my issue was but the default is write-back).  I've seen similar performance differences whether on a R10 array or R5.  I'm comparing like for like, except the disks in the SAN are standard HP 2.5" SFF and the servers are SC drives but don't expect this much of a difference.  I have older DL380 G7s with local disks and these are out-performing both the SAN and the SC disks but I'm not concerned with this at present.

Can anyone offer any suggestions? I've recently upgraded the firmware on the SAN, I don't know if it was an issue previously as I didn't test it.  I've read somewhere about configuring the Emulex cards window send size but not sure how to do this on a Windows server and also if its even relevant.

Thanks in advance.

[Dazza76]

Also when copying large files to the SAN i saw the disk write bytes/sec go up to about 200MB/s anddown to 0B/s in a sort of sawtooth which I don't see with DAS.

See attached,

Anybody offer any suggestions?