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List:       aic7xxx
Subject:    AHA 2940UW performance
From:       Metod Kozelj <metod.kozelj () rzs-hm ! si>
Date:       2000-03-29 12:42:23
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Hello,

a while ago I was wondering myself why wouldn't AHA 2940UW and Seagate
ST39175LW talk to each other faster than 20MByte/sec. As my box is alpha,
I couldn't just check the settings in SCSI BIOS. I only got one reply
saying that I better find some x86 PC, stick the card in it and check the
settings.

I did it and I found out that Ultra was disabled, so the highest speed
possible to negotiate was 20MBytes/sec. After I changed it to enable Ultra
speeds, the drive and AIC started to talk to each other at 40MBytes/sec,
which really improves the performance (using hdparm -t it increases from
13.63 to 18.97 MBytes/sec).

I know that this issue is a very minor one for majority of linux users
(those who are running linux on some kind of x86 PC). It is quite an issue
for me and others running linux on alphas (and any platform other than
x86 I imagine). I had to shut-down three machines, pull out the card,
stick it to some x86 PC, run SCSI BIOS setup and replace the card to
alpha box. All three cards had ultra speed disabled (factory
default. SIC!) and machines are production ones. Plus I had some
problems to find some x86 PC (they are quite rare in our department).

I know that it's a Good Thing for driver to respect SCSI BIOS settings.
But, couldn't there be some option to force driver use other limit values?

I would guess it would be quite hard to make some utility to actually
change settings on the card while running linux (on, say, alpha).

Regards,
  Metod

Metod Kozelj

mailto:Metod.Kozelj@rzs-hm.si            /\  Ne posiljajte mi smeti ker grizem!
http://www.rzs-hm.si/                   /  \  Don't spam me for I bite!
_______________________________________/    \__________________________________

---- perl -e 'print $i=pack(c5,(41*2),sqrt(7056),(unpack(c,H)-2),oct(115),10);'



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