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From: pa1159@sdcc13.ucsd.EDU (pa1159)
Newsgroups: comp.arch
Subject: Re: *big iron*
Message-ID: <1186@sdcc13.ucsd.EDU>
Date: 29 Sep 89 00:54:17 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> <24950@lou
Reply-To: pa1159@sdcc13.ucsd.edu.UUCP (pa1159)
Organization: Univ. of California, San Diego
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In article <24950@louie.udel.EDU> nelson@udel.EDU () writes:
>In article <22488@cup.portal.com> cliffhanger@cup.portal.com (Cliff C Heyer) writes:
>>
>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.
>

This brings up a point:  in what processing regimes does total
sustained disk tranfer rate be the performance-limiting factor?

For a mini/single-user workstation configuration I'd think that the
average access time rather than sustained throughput would be most
important as most I/O transfers would be relatively small.

So, given equal access times, how much of a difference in
interactive workloads does a jump from say 500 KB/s (low end micro
disks) to 3-4 MB/s make in performance?

Of course, for things like massive image processing applications 
sustained throughput is a Good Thing, but for the Rest Of Us, how
much does it really matter?

Matt Kennel
pa1159@sdcc13.ucsd.edu

PS:  The Connection Machine parallel disk subsystem is pretty nifty.
40 simultaneous bitstreams, which when error-corrected &c make a
32-bit word per tick.  You can trash one drive and then reconstruct
its contents from the 39 others.

I don't know the numbers, but I suspect that it's very fast.


l>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