I am looking for some information about the
speed of an IBM ESS 2105-800 (shark) disk subsystem,
connected to an IBM pSeries (AIX 5.2-ML2)
with 2 Gigabit Fibre Channel (SAN Switch 2109-F32).

I tested with:

time dd if=/dev/$DEVICE of=/dev/null bs=128k count=10000

a)
DEVICE=hdisk0 # internal SCSI-disk (10000rpm):
30 MB/s

b)
DEVICE=hdisk0 # internal SCSI-disk (15000rpm):
45 MB/s

c)
DEVICE=vpath0 # ESS-LUN (SSA-disks, 15000rpm, RAID5 over an array/8-Pack):
22 MB/s

All values seem to be independent from blocksize (4k to 1024k)

Is the ESS really slower than a single SCSI-disk?

Is my test procedure wrong?

Thanks in advance.