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Path: utzoo!utgpu!water!watnot!watmath!clyde!rutgers!ames!cit-vax!mangler
From: mangler@cit-vax.UUCP
Newsgroups: comp.arch
Subject: Re: disk performance benchmarks.
Message-ID: <2102@cit-vax.Caltech.Edu>
Date: Fri, 20-Mar-87 22:20:04 EST
Article-I.D.: cit-vax.2102
Posted: Fri Mar 20 22:20:04 1987
Date-Received: Sun, 22-Mar-87 22:45:34 EST
References: <307@sunlamp.UUCP> <7759@utzoo.UUCP>
Organization: California Institute of Technology
Lines: 18
Summary: 60% seeks

In article <7759@utzoo.UUCP>, henry@utzoo.UUCP (Henry Spencer) writes:
> There is a conjecture hereabouts -- not verified
> by experiment, mind you -- that on a busy multi-user system, the increase
> in block size accounts for 100% of the performance improvement, with things
> like cylinder groups contributing absolutely nothing.

On the 4.2bsd vaxen that I run, 2/3 of the disk transfers require a seek,
and judging from the average transfer time of about 26ms, the seeks are
fairly long.  (These statistics from a modified disk driver & iostat).

When dumping every file on the disk to tape, our vax-780 with its 4K
blocksize gets only about twice the disk throughput of the 3b20 sitting
next to it doing 1K reads.

I'd say Henry is understating his point.  Although, even a factor of two
can be useful at times...

Don Speck   speck@vlsi.caltech.edu  {seismo,rutgers,ames}!cit-vax!speck