Adaptect raid performance with FreeBSD

[Ari Suutari]

Hi,

I have been wondering if my disk setup should perform better than
it is now doing. 

I have a dual PIII 500 Mhz with intel server mother board.
(a couple of years old). On that, I have DPT (or currently Adaptec)
raid controller "DPT PM2654U2", which supports 40 Mhz SCSI bus,
giving a theoretical data transfer speed of 80 MB/s. There are
two physical disks, which have been mirrored (ie. raid-1).
The disks are maxtor atlas 10K4, I think that maxtor tells
that they should give sustained transfer rate up to 72MB/s.
I have confirmed that SCSI bus is at 80MB/s speed
with dptutil.

The system is running FreeBSD 4.8.

However, when reading raw device with dd like this:

dd if=/dev/rda1s1a of=/dev/null bs=1m count=100
100+0 records in
100+0 records out
104857600 bytes transferred in 4.193832 secs (25002814 bytes/sec)

So, I get only about 25MB/s. Shouldn't I be getting something
like 70 MB/s, or even more since there are two disks that
can server read requests ?

Maybe there is something I could tune ? The BIOS doesn't
have much, there is only setting to enable bus mastering (enabled)
and another for pci latency timer values (was 40, I think)


	Ari S.


-- 
Ari Suutari
Lemi, Finland