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From: ekalenda@cup.portal.com (Edward John Kalenda)
Newsgroups: comp.periphs.scsi
Subject: Re: Separate controllers to enhance performance?
Message-ID: <41745@cup.portal.com>
Date: 27 Apr 91 06:56:00 GMT
References: <1991Apr26.174456.810@homecare.uucp>
Organization: The Portal System (TM)
Lines: 26

>I'm not real familiar with SCSI drives so I have a question about their
>performance (actually it's on the controller).  When you run MFM or RLL,
>the controller can only read or write one device at a time whether it is
>a hard drive or floppy.  One database vendor suggested putting database
>files or separate hard drives to increase performance.  I protested that
>it wouldn't make any difference unless the drives were on separate
>controllers.  Does this apply to SCSI controllers as well or does it
>access drives simultaneously (or almost so)?

The performance improvement the vendor was talking about comes from not
having to move the heads as much. If you are accessing two files, the
heads would bounce back and forth between them. If they are on seperate
drives, they would not move as much.

Another improvement comes from the fact that there would be less
fragmentation since the files would grow on seperate volumes, so they
would not interleave eacch other during growth.

Using seperate controllers (MFM, RLL or SCSI) would only help if the
operatin system was smart enough to have them both active at the same
time and the hardware had enough DMA channels (and speed) to be doing
multiple DMAs. If your using DOS it's got no brains for this. Unix can
do it in some implementations.

Ed
ekalenda@cup.portal.com