LSI megaraid sas performance

Hello,

We are testing the LSI 8480E SAS RAID controller with the following setup:
- Dual XEON server, 1 GB RAM
- 12 SATA II disks in Promise J300S SAS JBOD connected with a single x4 SAS cable
- stripe size is 64k, write back caching enabled

Measured with IOMETER. First two values are for read/write with 64 kb block size with sequential I/O. Default test is RANDOM I/O 2/3 read + 1/3 write at 2k block size.

- Windows 2003 Server-64 bit:
RAID 0 - R: 606 MB/s, W: 335 MB/s, Default: 820 IOPS RAID 5 - R: 593 MB/s, W: 304 MB/s, Default: 475 IOPS //RAID 0 write should be better but otherwise ok

- Linux 2.6.16.9-64 bit:
RAID 0 - R: 165 MB/s, W: 373 MB/s, Default: 76 IOPS RAID 5 - R: 147 MB/s, W: 285 MB/s, Default: 74 IOPS

READ performance is bad. Random I/O is like a single disk. The 8408 (internal version) shows the same behaveour. Has anyone else results for this controller or suggestions to improve this?

Thanks,
Mirko