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From: terry@cs.weber.edu (A Wizard of Earth C)
Subject: Re: [386BSD] What SCSI controllers _are_ supported?
Message-ID: <1993Feb19.033337.13588@fcom.cc.utah.edu>
Keywords: 386BSD SCSI
Sender: news@fcom.cc.utah.edu
Organization: Weber State University (Ogden, UT)
References: <C2Luz6.1CzA@austin.ibm.com> <1993Feb17.214948.9390@fcom.cc.utah.edu> <C2no1H.1JDo@austin.ibm.com>
Date: Fri, 19 Feb 93 03:33:37 GMT
Lines: 54
In article <C2no1H.1JDo@austin.ibm.com> guyd@austin.ibm.com (Guy Dawson) writes:
>
>I've no problem with a cache controller being a big win for DOS...
[ ... ]
>> You may see some slight improvement on sequential reads; on the other hand,
>> Julians driver supports sufficiant optimizations in the way controllers are
>> used to make predictive read-ahead on a cached SCSI controller almost a 0
>> win.
>
>You are saying that with Julians drivers there is no gain?
>
>That is what I am saying...
This is what I believe; the biggest win here will be async reads to match
the existing async writes.
[ ... list of potential benefits ... ]
>Again I have no problem believing the benefits that DOS obtains. Its with
>BSD ( ie good Unix ) that I'm questioning their use.
Right; the benefits I was referring to were for 386BSD or UNIX, not DOS; I
brought up DOS to say "this is what it's supposed to do" as opposed to what
it will do under 386BSD.
>With a BSD program, if you execute the program, count to 10, or 100 and
>re-execute the program you will almost certinally read the file from
>the BSD cache... No cache can help you the first time you execute a
>program.
Well, yes, of course.
>I suspect that if we got face to face we would violently agree!
I think we can violently agree on the net if we work at it! 8-).
My opinion unsubstantiated by testing: A cached controller is useless
for anything other than slowing initial transfer rates unless the controller
cache is *much* larger than the UNIX cache *and* the transfer rate between
the controller cache and memory is the same as that between memory and
memory. Spend your money on something you can see, like a big monitor.
Terry Lambert
terry@icarus.weber.edu
terry_lambert@novell.com
---
Any opinions in this posting are my own and not those of my present
or previous employers.
--
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