Sda: For Cache Data Failed

We just upgraded our server with 8 brand new seagate cheetah 15k.5's, a battery backup unit, and a 256mb dimm for the raid controller. In the boot process, i noticed an error about caching or something.

After analyzing the dmesg log, i found the error:
sda: asking for cache data failed
sda: assuming drive cache: write through

It seems like the kernel can't get to the raid controllers cache, so it switches to the write through setting.

I've benchmarked the harddisks with the write through, and write back setting. The odd thing is that both settings deliver the same performance.

Normally, write back increases the performance with like 100%... That's why we bought the battery backup unit.

So something is going wrong, but where lays the problem?

Server:

Quote:

8 X seagate cheetah 15k.5, U320, 16mb cache, SCA, 73GB
1 X chenbro backplane, U320, SCA, 2 channels, 8 ports
1 X LSI megaraid 320-2x raid controller, U320, 2 channels, battery pack and 256 upgraded dimm
6 GB DDR PC3200, ECC, CL3
2 X AMD opteron dual cores (4 X 2.0 ghz)