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From: mangler@cit-vax.Caltech.Edu (Don Speck)
Newsgroups: comp.periphs
Subject: Re: Wanted: SCSI Disks for Sun3's
Message-ID: <4190@cit-vax.Caltech.Edu>
Date: Thu, 15-Oct-87 02:29:47 EDT
Article-I.D.: cit-vax.4190
Posted: Thu Oct 15 02:29:47 1987
Date-Received: Sat, 17-Oct-87 02:11:40 EDT
References: <128@quick.COM> <536@micas.UUCP> <5395@jade.BERKELEY.EDU>
Organization: California Institute of Technology
Lines: 32
Summary: disconnect/reconnect works

In article <536@micas.UUCP> jvs@micas.UUCP (Jo stockley) writes:
>Also while I'm about it why the hell
>did Sun ever produce a SCSI board that does nopt support DIS/RE CONNECT
>and then supply it in a multi user system???

I recently had a chance to benchmark SCSI I/O on a Sun 3/60FC
running SunOS 3.4 with Sun 141 MB ESDI disks.

Running 'dump' to /dev/null (most disk-intensive program handy)
on one disk at a time did 34 transfers per second; two at once
did 30 transfers per second per disk:  evidence of properly
working disconnect/reconnect.  dump or tar (!) to SCSI tape
would stream using the default (10K) blocksize, but not using
the Sun-recommended 63K blocksize, implying that the (Emulex)
SCSI tape controller has a small write-behind buffer.  4.3bsd
dump (overlaps disk & tape I/O) would stream the tape with any
blocksize, further evidence of disconnect/reconnect working.

I measured the minimum time between 1K reads and larger reads,
from which I derive the value of 'rotdelay' (about 8ms) and,
more importantly, break down the blocksize-dependent part of
read setup and recovery time.  Recovery time had a significant
dependence on blocksize; assuming this is due to DMA having
to catch up with the disk transfer rate, it implies a DMA
rate of 0.8 MB/s.  Disk controller buffering was sufficient
to not 'blow a rev' in the middle of a transfer, even on reads
of a couple of tracks.

Conclusion:  though not as fast as an Eagle, it's comparable
in speed to typical big disks such as the DEC RA81.

Don Speck   speck@vlsi.caltech.edu  amdahl!cit-vax!speck