[K12OSN] Woe is me: Onboard SCSI/RAID Controller

Robert Arkiletian robark at telus.net
Tue Oct 12 18:19:26 UTC 2004

Hi Debbie,
I have good news. I am using this SCSI controller chip AIC7902W with super
stability/performance in my school. I researched the chip before I bought it. It
has very affordable scsi performance.

I got an intel server board with the chip. The docs say it supports HOST raid.
However, Linux does NOT support Host Raid. Host raid is actually software raid
for Windows (ITS NOT HARDWARE RAID). There are drivers for Windows to make it
work but not for Linux. However, the linux kernel will support software raid
using LVM, which is just as fast as some hardware raid setups. (Although I have
not tried it, I know it's done when you setup your partitions) The beautiful
aspect of the AIC7902W is that is has TWO scsi channels. So you can have the
full throughput of each channel and raid them through the kernel. All I did was
use one scsi drive for / and another for /home. I have not tried raid. I'm using
k12ltsp 3.1.2 (redhat 9) and not 4.1.1 (FC2). 32 clients == no problem.

A couple of notes. You MUST disable HostRaid in the bios for the controller to
work with Linux. Also, I down graded each scsi channel to 160 mb/s instead of
the 320 mb/s (default). The system was not fully stable at 320mb/s because of
scsi driver issues. Don't worry though a new 10k rpm scsi drive only needs
around 60 mb/s bandwidth. So you should be okay for about 3 drives/channel at
full throttle for all of them (highly unlikely). I don't think you will ever
need more than 6 scsi drives for k12ltsp. The driver for the kernel is written
by Justin Gibbs. He had some issues/disagreements with James Bottomley (kernel
maintainer) and Linus Torvalds. So he pulled the drivers before version 2.0.x
from his site. The 2.6 series kernel has stable adaptec scsi aic79xx driver
1.3.x in it. But if you go with k12ltsp 4.0.1 (FC1 & kernel 2.4.22) or earlier
you will have to use a driver update disk (DUD) from here (versin > 2.0)


these are stable too but the kernel maintainers are wary of them for technical
reasons beyond my comprehension.

This DUD disk has to be made with "dd" and must be used during installation of
the OS in Expert mode.
If you go with k12ltsp 4.1.1 (FC2) , no worries, it has stable scsi adaptec
aic79xx driver 1.3.x built in since it comes with kernel 2.6.5
If I was you, I would go with k12ltsp 4.1.1 (FC2) from the beginning. It will be
the easiest for you. I did not have this option when I started. Just don't
forget to disable HostRaid in the SCSI bios and lower the throughput to 160mb/s
for each channel and you should be good to go. Also make sure your scsi cables
are high quality and terminated properly.

Hope that helps
Good luck

BTW the drivers on adaptec/intel sites are very old (don't use them)

Robert Arkiletian

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