IBM DS3400 speed issue

[SpaceHonkey]

Well I'm looking for help here after being turned away by IBM.

To keep it short - write speeds are not what I'd expect them to be. For the purpose of simplicity, I'll only discuss one server in question.

I have setup two example luns, one on a 5 300GB 15K SAS disk RAID5 array, another on a 2 300GB 15K SAS disk RAID0 array. Using IO meter, sequential read/write I tested with block sizes from 2KB to 4MB. Max performance is seen with 2MB blocks. Tests performed with no other activity on the SAN.

RAID5 Lun - Read = 349MB/s, Write = 90MB/s
RAID0 Lun - Read = 232MB/s, Write = 73MB/s

Please tell me this isn't normal.

About the DS3400, 4GB FC, dual storage processors - and yes write caching is enabled on all luns.

Any suggestions? IBM kicked me to the curb...

[SpaceHonkey]

I also just tried disabling write caching on the RAID0 lun for grins, and the speed only dropped to 67MB/s.

[sphinx99]

How many channels to the host(s) you're testing with? 349MB/sec is pretty good for a single 4GB fiber pipe.

[SpaceHonkey]

Two. Read performance is not my concern. Write performance is 25-30% of read - that's the issue. It seems as if it's not really using write caching. Also, write caching is enabled on the host server too.

Other hosts, VMware ESX, have the same issue.