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From: kirchner@informatik.uni-kl.de (Reinhard Kirchner)
Newsgroups: comp.arch
Subject: Disk with 2 HDA ( Was: Re: disk rotation speed
Message-ID: <6308@uklirb.informatik.uni-kl.de>
Date: 3 Aug 90 11:37:33 GMT
References: <WAYNE.90Aug2143750@dsndata.uucp>
Sender: news@uklirb.informatik.uni-kl.de
Lines: 21

From article <WAYNE.90Aug2143750@dsndata.uucp>, by wayne@dsndata.uucp (Wayne Schlitt):
> 
> I have wondered about this for a long time.  Are there many drives
> with more than one actuators?  Why arent there more?
> 
As far as I know the only drives with two HDA ( Head-Disk-assembly )
are large blue ones like 3380, 3390 I don't know. Even on the 3380
the to heads do not overlap, they are two drives on one spindle and one
stack of platters.

Somewhere I read that this gives more reliability than two drives with
two motors etc.

Two overlapping indepenant HDAs on one drive may give a lot of trouble
to the operating system. We may now have one drive at two controllers
and to channels, but then the drive is busy when one controller uses it.
With two independant HDA we have totally asynchronous access to the same data!

R. Kirchner
Univ. Kaiserslautern, Computer Science
kirchner@informatik.uni-kl.de