Path: utzoo!attcan!utgpu!utstat!jarvis.csri.toronto.edu!rutgers!cs.utexas.edu!uunet!mcvax!kth!draken!ttds!jonasn
From: jonasn@ttds.UUCP (Jonas Nygren)
Newsgroups: comp.arch
Subject: Re: DMA on RISC-based systems
Message-ID: <1213@ttds.UUCP>
Date: 8 Jun 89 11:13:06 GMT
References: <46500067@uxe.cso.uiuc.edu> <181@dg.dg.com> <185@dg.dg.com> <8479@june.cs.washington.edu>
Reply-To: jonasn@ttds.UUCP (Jonas Nygren)
Organization: The Royal Inst. of Techn., Stockholm
Lines: 27

In article <8479@june.cs.washington.edu> rik@june.cs.washington.edu (Rik Littlefield) writes:
>In article <185@dg.dg.com>, rec@dg.dg.com (Robert Cousins) writes:
>< Given that a disk channel will be averaging 200K bytes/second ...
<deleted>
>< Comments?
>
>The methodology seems sound, but I question the numbers.  Just guessing,
>but I suspect that workstation class systems have an *average* disk
>throughput that is at least 10X lower than this number, even when
>they are working full out.  (Remember that 200K bytes/second is
>720 Mbytes/hour.)  If so, then the value of DMA is also 10X lower.  
>
>Would someone with real utilization numbers care to fill us in?
>
>--Rik

I have performed a small test on a DECstation3100 with a RZ55-230 Mb disk.
The test used 15 processes reading/writing 2Mb files each, with the following
results:

Write 15x2 Mb: 113 s, 265 kb/s
Read 15x2 Mb:  117 s, 256 kb/s
Read 15x2 + write 15x2 Mb (new and in parallell): 281 s, 213 kb/s

Mean value: 234 kb/s

/jonas