Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!haven!udel!nelson
From: nelson@udel.EDU
Newsgroups: comp.arch
Subject: Re: *big iron*
Message-ID: <24950@louie.udel.EDU>
Date: 27 Sep 89 03:05:08 GMT
References: <21962@cup.portal.com> <1989Sep12.031453.22947@wolves.uucp> <22130@cup.portal.com> <1989Sep16.044013.429@wolves.uucp> <259@ssp1.idca.tds.philips.nl> <22308@cup.portal.com> <7981@cbmvax.UUCP> <11538@burdvax.PRC.Unisys.COM> <22488@cup.portal.com>
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In article <22488@cup.portal.com> cliffhanger@cup.portal.com (Cliff C Heyer) writes:
>
>I'm talking about sustained rates *per job*, not for the *system*. I know
>overall throughput is in excess is 100MB/sec. But who makes a disk drive that
>does 100MB/sec transfers? The best now is 3-4MB/sec. So when we get right
>down to it, a COBOL program reading a file can expect less than 3-4MB/sec on
>a mainframe. (The same reasoning explains how a 100 MIPS 4 processor mainframe
>can only support 25 MIPS *per job*)
>
Since we are talking about "*big iron*", let's talk about real big iron.
Cray DD-40 disk drives can support >10MB/sec through the operating
system (at least COS; I assume the case is also true for UNICOS).
And COS also supports disk striping at the user level, so for
sequential reads of a file striped across an entire DS-40 disk
subsystem (20+ GB, 4 drives) a process can achieve sustained rates
of 40MB/sec.  Of course, this is for relatively large (~ 0.5MB)
reads, but these aren't uncommon for the sort of processing Crays
do.

Disk I/O is one of Cray's big selling points vs. the Japanese
super-computer manufacturers--their machines generally have
mainframe (read 4MB/sec) style disk channels.

Mark Nelson                 ...!rutgers!udel!nelson or nelson@udel.edu
This function is occasionally useful as an argument to other functions
that require functions as arguments. -- Guy Steele