Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!bloom-beacon!mit-eddie!uw-beaver!uw-june!uw-entropy!uw-apl!grace!quick!srg
From: srg@quick.COM (Spencer Garrett)
Newsgroups: comp.arch
Subject: Re: Why no disks with two HDAs ?
Keywords: diskdrives, headdiskassemblies
Message-ID: <234@quick.COM>
Date: 22 Jun 88 08:25:35 GMT
References: <2351@uklirb.UUCP> <2440@winchester.mips.COM>
Organization: Quicksilver Engineering, Seattle
Lines: 13


A big reason for not putting in two HDA's is that you would then
have to align them.  One big advantage of non-removable media
is that as long as the heads don't move (WRT one another) it
doesn't matter where they are.  You just torque them down and
format the drive.  It is possible to get around this with
embedded-servo information, but then changing heads requires a
(short) seek, which does nasty things to filesystem throughput.
(The cylinders get very small, equal to one track apiece.)
It's a shame, too, because having multiple access arms could
otherwise give you the best of both worlds (one big drive, for
allocation efficiency and flexibility, versus several drives
with the ability to seek independently).