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From: guyd@austin.ibm.com (Guy Dawson)
Subject: Re: [386BSD] What SCSI controllers _are_ supported?
Originator: guyd@pal500.austin.ibm.com
Sender: news@austin.ibm.com (News id)
Message-ID: <C2pFB0.JDB@austin.ibm.com>
Date: Fri, 19 Feb 1993 16:33:00 GMT
References: <C2Luz6.1CzA@austin.ibm.com> <1993Feb17.214948.9390@fcom.cc.utah.edu> <C2no1H.1JDo@austin.ibm.com> <1993Feb19.033337.13588@fcom.cc.utah.edu>
Organization: IBM Austin
Keywords: 386BSD SCSI
Lines: 65
In article <1993Feb19.033337.13588@fcom.cc.utah.edu>, terry@cs.weber.edu (A Wizard of Earth C) writes:
> 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-).
>
True - it was realy a moan about the low band width of posting vs. talking
at the coffe machine.
>
> 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.
Now I agree with that. If ones Unix cache is too small then more cache
anywhere helps. I made the assumption that the Unix cache was well
sized...
>
>
> Terry Lambert
> terry@icarus.weber.edu
> terry_lambert@novell.com
Guy
--------------------------------------------------------------------------------
Guy Dawson - Hoskyns Group Plc.
guyd@hoskyns.co.uk Tel Hoskyns UK - 71 251 2128
guyd@austin.ibm.com Tel IBM Austin USA - 512 838 3377
"Knolege is powef, Speling is unimportnt" via Pete W. De Bonte