Path: utzoo!attcan!uunet!husc6!mailrus!ames!elroy!cit-vax!mangler
From: mangler@cit-vax.Caltech.Edu (Don Speck)
Newsgroups: comp.unix.wizards
Subject: Re: Vax 11/780 performance vs Sun 4/280 performance
Summary: I/O throughput
Message-ID: <6926@cit-vax.Caltech.Edu>
Date: 13 Jun 88 08:58:03 GMT
References: <22957@bu-cs.BU.EDU> <14968@brl-adm.ARPA> <601@modular.UUCP> <7331@swan.ulowell.edu> <2282@rpp386.UUCP>
Organization: California Institute of Technology
Lines: 25

I am reminded of this article from comp.arch:

In article <44083@beno.seismo.CSS.GOV>, rick@seismo.CSS.GOV (Rick Adams) writes:
> Well, to start with I've got a Vax 11/780 with 7 6250 bpi 125 ips
> tape drives on it. It performs adequately when they are all running.
> I STILL haven't found anything to replace it with for a reasonable amount
> of money. Nothing in the Sun price range can handle that I/O volume.

I've seen a PDP-11/70 with eight tape drives, too.

And as Barry Shein said, "An IBM mainframe is an awesome thing...".
One weekend, noticing the 4341 spinning a pair of GCR drives at over
half their rated 275 ips, I was shocked to learn that it was reading
the disk file-by-file, not track at a time.  BSD filesystems just
can't compare to what this 2-MIPS machine could do with apparent ease.

How do they get that kind of throughput?  I refuse to believe that it's
all hardware.  Mainframe disks rotate at 3600 RPM like everybody else's
and their 3 MB/s transfer rate is only slightly higher than a SuperEagle.
A 2-MIPS CPU would be inadequate to run a BSD filesystem at those speeds,
so obviously their software overhead is a lot lower, while at the same
time wasting no disk time.  What is VM doing efficiently that Unix does
inefficiently?

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