Adaptec 2810SA extremely fast or extremely slow?

Hi, sorry for bad english..
I've got a Tyan Thunder S2885 and an Adaptec 2810SA, configured as
follows:

- 5 Maxtor 300gb hard disks on adaptec card
- 1 Maxtor 160gb hard disk attached to the motherboard
- 3 RAID5 volumes (partitions) on adaptec card
- 1 partition 1TB
- 1 partition 160 GB
- 1 partition 5GB

After executing a benchmark test, the results surprised me...

All the volumes of the Adaptec card showed the same results:
__________________________________________________ __________
READ
- sequential read (large files):
- random read (large files):

- sequential read (small files):
- random read (small files):

__________________________________________________ __________
WRITE
- sequential write (large files):
- random write(large files):

- sequential write(small files):
- random write(small files):



Aren't these results strange for what is said to be an "ideal cost-
effective solution for applications where high levels of sustained
read and write performance are required, including video streaming,
web content, reference data and fixed content storage" ??

Thanks a lot,
Marco