Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!ames!sgi!markb@denali.sgi.com
From: markb@denali.sgi.com (Mark Bradley)
Newsgroups: comp.periphs
Subject: Re: Synchronous SCSI *Disks*
Summary: Be Patient on High Speed disks--they're coming.
Message-ID: <39033@sgi.SGI.COM>
Date: 27 Jul 89 22:37:03 GMT
References: <29254@ames.arc.nasa.gov> <257@odin.SGI.COM> <29289@ames.arc.nasa.gov>
Sender: daemon@sgi.SGI.COM
Organization: Silicon Graphics, Inc., Mountain View, CA
Lines: 47

In article <29289@ames.arc.nasa.gov>, lamaster@ames.arc.nasa.gov (Hugh LaMaster) writes:
> In article <257@odin.SGI.COM> olson@anchor.sgi.com (Dave Olson) writes:
> >lamaster@ames.arc.nasa.gov (Hugh LaMaster) writes:
> 
> >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 
> 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.
> 

They are coming.  Although I can't give names and dates, think in terms
of multiple HDA's under the control of a single embedded controller with
significant 'cache' on board.  Multihead/surface disks in 5.25 or 3.5 inch 
form factor probably don't make sense, but there are ways other than that to
get significantly faster raw data rates from disks.

24 MHz drives are just around the corner without ZBR techniques, as well.

It is important to realize, too, that just because the disks are fast
that the file systems out there in unix land today can really deliver
the read performance that the hardware can provide.  Advances are being
made to take advantage of this faster technology too, but they must
be developed together in order for it all to work. 

We'll have something for you soon.

					markb

 
--
Mark Bradley				"Faster, faster, until the thrill of
IO Subsystems				 speed overcomes the fear of death."
Silicon Graphics Computer Systems
Mountain View, CA			     ---Hunter S. Thompson