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From: olson@anchor.sgi.com (Dave Olson)
Newsgroups: comp.periphs
Subject: Re: Synchronous SCSI *Disks*
Message-ID: <257@odin.SGI.COM>
Date: 27 Jul 89 07:39:44 GMT
References: <29254@ames.arc.nasa.gov>
Sender: news@odin.SGI.COM
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lamaster@ames.arc.nasa.gov (Hugh LaMaster) writes:

>I keep seeing all these ads for synchronous SCSI controllers with speeds
>in the 4-5 MB/sec. range.  But I don't see the ads for 4-5 MB/sec.
>synchronous SCSI disks.  Are there any reasonably inexpensive general
>purpose high capacity etc. synchronous SCSI disks out there with speeds of,
>well, what is available?

These speeds are typically the burst speeds over the scsi bus
when talking about disks; devices that transfer from/to RAM might
actually be able to sustain them.

There are disks coming on the market now or in the next 2-3 months
that are 20 Mhz drives and can deliver sustained 2.1Mb/sec
on read, and 1.9Mb/sec on writes, when doing i/o on contiguous
files with 128K or larger read/write size on the raw device; less,
but not too much lower with sizes down to about 16K.
Filesystem rates are typically lower...

Some of these drives actually can deliver bursts from/to their
buffer at 5Mb/sec as measured with a logic analyzer, for 32K to 64K
at a time.  (Some of these drivers are zone bit recording drives,
so the throughput drops off as you near the end of the drive.)

Of course, your host has to be able to handle it also; the new
Silicon Graphics 4D25 (20 MHz Personal Iris) with the WD 33C93A
SCSI chip is the machine on which the above throughput was measured.

	Dave Olson

It's important to keep an open mind, but not so open
that your brains fall out. -- Stephen A. Kallis, Jr.