Filesystem benchmarking for pg 8.3.3 server

Hello list,

I have a server with a direct attached storage containing 4 15k SAS
drives and 6 standard SATA drives.
The server is a quad core xeon with 16GB ram.
Both server and DAS has dual PERC/6E raid controllers with 512 MB BBU

There is 2 raid set configured.
One RAID 10 containing 4 SAS disks
One RAID 5 containing 6 SATA disks

There is one partition per RAID set with ext2 filesystem.

I ran the following iozone test which I stole from Joshua Drake's test
at

http://www.commandprompt.com/blogs/joshua_drake/2008/04/is_that_performance_i_smell_ext2_vs_ext3_on_50_spindles_testing_for_postgresql/

I ran this test against the RAID 5 SATA partition

#iozone -e -i0 -i1 -i2 -i8 -t1 -s 1000m -r 8k -+u

With these random write results

    Children see throughput for 1 random writers     =  168647.33 KB/sec
    Parent sees throughput for 1 random writers     =  168413.61 KB/sec
    Min throughput per process             =  168647.33 KB/sec
    Max throughput per process             =  168647.33 KB/sec
    Avg throughput per process             =  168647.33 KB/sec
    Min xfer                     = 1024000.00 KB
    CPU utilization: Wall time    6.072    CPU time    0.540    CPU
utilization   8.89 %

Almost 170 MB/sek. Not bad for 6 standard SATA drives.

Then I ran the same thing against the RAID 10 SAS partition

    Children see throughput for 1 random writers     =   68816.25 KB/sec
    Parent sees throughput for 1 random writers     =   68767.90 KB/sec
    Min throughput per process             =   68816.25 KB/sec
    Max throughput per process             =   68816.25 KB/sec
    Avg throughput per process             =   68816.25 KB/sec
    Min xfer                     = 1024000.00 KB
    CPU utilization: Wall time   14.880    CPU time    0.520    CPU
utilization   3.49 %

What only 70 MB/sek?

Is it possible that the 2 more spindles for the SATA drives makes that
partition soooo much faster? Even though the disks and the RAID
configuration should be slower?
It feels like there is something fishy going on. Maybe the RAID 10
implementation on the PERC/6e is crap?

Any pointers, suggestion, ideas?

I'm going to change the RAID 10 to a RAID 5 and test again and see
what happens.

Cheers,
Henke