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From: cdr@amdcad.AMD.COM (Carl Rigney)
Newsgroups: comp.periphs
Subject: Re: Synchronous SCSI *Disks*
Keywords: scsi, scsi-2, ciprico, wren, raid
Message-ID: <26514@amdcad.AMD.COM>
Date: 28 Jul 89 04:37:39 GMT
References: <29254@ames.arc.nasa.gov> <307@wombat.UUCP>
Reply-To: cdr@amdcad.UUCP (Carl Rigney)
Organization: Advanced Micro Devices
Lines: 36

Ciprico's latest SCSI VME board supports the SCSI-2 wide standard.  With a 32bit
data path instead of 8bit it should reach 20 MByte/sec synch burst rates.
I believe Imprimis either has or is about to have some drives that do wide
SCSI.  I suspect the problem will be finding hosts that can accept that
kind of data input.

CDC Wren V's (600 MB formatted, 16ms, 5MB synch) are selling for around $2500; 
I've also heard good things about the Hitachi that someone else mentioned.

Ciprico said at Sun-Expo that they expect Fast SCSI-2 chips to come on the
market in January, and they expect to have a board using them by April or so.
Fast, Wide SCSI is 40 Megabytes/Sec!  At that point you probably have to talk
RAID to get the necessary disk speed.

	--Carl Rigney

Glossary for those who are confused:  SCSI-1 standard uses a 50-pin
connector with 8 data lines.  SCSI-2 defines a "wide" implementation
that has a second cable with 8 or 24 additional data lines, doubling or
quadrupling your data rate.  SCSI-2 also defines a "fast"
implementation that tightens up the timings to allow 10 MB synch on the
old cables, or 40MB if combined with the 32-bit path.

A "RAID" is a set of parallel disks with striping by word, typically,
and usually a parity drive.  By using 5 disks (1 parity) you can
quadruple your data rate; by using 9 you get 8x.  Some have the
capability to lose a drive and keep going, recreating the replacement
drive (after you swap out the bad one) off the Parity drive.  (Others
require downtime while it recreates the missing drive.)  Mean time to
Data Loss for RAIDS is astronomical because you have to lose two drives
at the same time.

Someone recently mentioned that NCR's "Introduction to SCSI" book is
now being published by Prentice-Hall - I'd recommend it highly.  I got
mine at Techmart after the IEEE conference on System Design & Mass
Storage last month; I don't know if they still have any.