Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!ames!ames.arc.nasa.gov!lamaster
From: lamaster@ames.arc.nasa.gov (Hugh LaMaster)
Newsgroups: comp.periphs
Subject: Re: Synchronous SCSI *Disks*
Message-ID: <29289@ames.arc.nasa.gov>
Date: 27 Jul 89 16:06:01 GMT
References: <29254@ames.arc.nasa.gov> <257@odin.SGI.COM>
Sender: usenet@ames.arc.nasa.gov
Organization: NASA - Ames Research Center
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In article <257@odin.SGI.COM> olson@anchor.sgi.com (Dave Olson) writes:
>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

>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.

>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

>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

I realize that the 4-5 MB/sec. is the SCSI bus rate, but, I guess what I am
asking is this: IBM, CDC, and more recently, SMD-E drives have been around,
(some of these for years) with speeds >= 3.0 MB/sec.  CDC and
Ibis have produced drives with data rates of 10-12 MB/sec 
(I know, parallel heads).  The need and technology are clearly there, 
though not necessarily in the same place (price/performance-wise).

My question is: now that "cheap" drives with data rates from a single head
of 24MHz are available, why aren't there synchronous SCSI drives with at
least such speeds available?  The new high speed workstations, like the
SGI 4D/25 mentioned by Dave Olson, are crying out for higher speed disks.

I believe that there would be probably be a market for a dual-parallel-head
drive which would effectively operate at 48MHz (2x24) and which could keep
a 5 MByte/sec SCSI bus busy.  About 4 of these would turn one of the new
20 MIPS workstations from various companies into a real "CDC 7600 on a desk".

  Hugh LaMaster, m/s 233-9,  UUCP ames!lamaster
  NASA Ames Research Center  ARPA lamaster@ames.arc.nasa.gov
  Moffett Field, CA 94035     
  Phone:  (415)694-6117