Xref: utzoo comp.sys.amiga.tech:5970 comp.sys.amiga:36212
Path: utzoo!censor!hugh
From: hugh@censor.UUCP (Hugh D. Gamble)
Newsgroups: comp.sys.amiga.tech,comp.sys.amiga
Subject: ST296N Interleave (was Re: Pal, Jr. HD controller info needed)
Summary: ST296N diskperf
Message-ID: <759@censor.UUCP>
Date: 3 Jul 89 04:12:54 GMT
References: <727@orbit.UUCP>
Organization: Bell Canada, Business Development, Toronto
Lines: 63

In article <727@orbit.UUCP>, baxt@pnet51.cts.com (Bill Backstrom) writes:
... 
> I have a B2000 with a 2090 and a ST296N (85 meg SCSI). I'm running
> 1.3, definitely using FFS (512 byte blocks) and version 34.4 of
> hddisk.  
> 
> Diskperf gives me a reads of about 80K bytes/sec and writes of 155K
> bytes/s for 32K blocks. I've also had an ST125 (20 meg ST-506) on the
> controller and got reads of 165K bytes/s and writes of 120K bytes/s. 
> Nothing special is going on - no hi-res with overscan and interlace,
> etc.
... 
> I have tried different interleaves, another 2090 card, and various
> partition sizes. Nothing has improved the performance. The only
> unusual thing I've noticed apart from the low data transfer rates is
> that I could not prep the drive with my controller, I had to use my
> dealer's 2090A. 
... 
> Bill Backstrom
> UUCP: {rosevax, crash}!orbit!pnet51!baxt
> ARPA: crash!orbit!pnet51!baxt@nosc.mil
> INET: baxt@pnet51.cts.com

Are you sure you actually got the interleaves you asked for?
Which ones did you try?

You may be having trouble because of S/W limitations or bugs,
or just through missing some subtlety in the documentation.
(There *is* documentation right? :-)

The fact that the ST125 came out faster shows you definitely
have something sub-optimal with the 296N setup.

You probably need an interleave of 4:1 for that drive.  I recall
a post a while back on C.S.A where someone said he'd managed to
get optimal performance on a ST296N at 3:1 interleave, but it took
some work.  I believe he had a 2090(A?), and I'm not sure what else it
took to get the interleave down.  Maybe an A2620 & setCPU & tuning
the cache buffers?

I have a 2000 with a 2620, and a 296N on a Comspec SA2000 non-DMA
SCSI controller.  On a stock 2000 Comspec recommends an interleave of
5:1 for the 296N and that comes as the default.  
I checked it, and that really is
the optimal interleave for that combination.  With the 2620, setCPU,
and a new PROM for the SA2000 that had optimizations for the '020,
I found I now get optimal performance (diskperf around 250K/s for
reading & writing) with an interleave of 4:1.

It seems that the ST296N needs a peculiarly high interleave for
either controller.  I haven't the faintest idea why.  Any guesses?

P.S. I left this cross posted to C.S.A & C.S.A.T. because I think
it's a .tech issue what's peculiar about the workings of the ST296N
that makes it different from most drives, but a user issue to note
that if you have one or get one you can expect best results with a high
interleave.  Continuations on this thread should go to whichever group
is most appropriate.
-- 
Hugh D. Gamble (416) 581-4354 (wk), 267-6159 (hm) (Std. Disclaimers)
hugh@censor, kink!hugh@censor
# It may be true that no man is an island,
# but I make a darn good peninsula.