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From: pcg@aber-cs.UUCP (Piercarlo Grandi)
Newsgroups: comp.unix.i386
Subject: Re: SCSI and 386/ix
Summary: two RLL controllers: fine, but some disadvantages...
Keywords: scsi 9380s under 386/ix
Message-ID: <1612@aber-cs.UUCP>
Date: 2 Feb 90 12:54:20 GMT
Reply-To: pcg@cs.aber.ac.uk (Piercarlo Grandi)
Organization: Dept of CS, UCW Aberystwyth
	(Disclaimer: my statements are purely personal)
Lines: 56

In article <25c77e8b:490.5comp.unix.i386;1@nstar.UUCP>
larry@nstar.UUCP (Larry Snyder) writes:

Me writes:

    >The real win is with *two* SCSI drives; while an RLL controller
    >usually is WD1003 compatible, and thus cannot possibly support
    >overlapped seeks or transfers, the ACB 1542 will support these,

He observes:

    How about getting 2 2372B RLL controllers each controlling 1 drive?
    Wouldn't this have the same effect as two SCSI drives on the 1542?

Yes, mostly. I have been considering doing this myself (I have
a 2372B with two 60MB discs, and for expansion I have
considered adding a second controller with another two discs).

There are some problems though:

* not all Unixes around support two controllers that easily,
especially if they are the same type;

* you don't get scatter-gather, which is a 1542 good idea (does
anybody apart from ISC exloit that?);

* you take up another backplane slot;

* two WD1003 style controllers, for a total of four discs, is
the maximum you can have, while SCSI is essentially unlimited
(in theory);

* if you want a tape, a SCSI controller that can drive all your
peripherals is cheaper and takes many less slots.

Also, I am not sure that the drivers that support two WD1003
compatible controllers do so in the right way, that is as
independent entities, with independent sort queues, parallel
operations, etc...

If you have a spare 2372B lying around, by all means try adding
it. I think that should make at least a noticeable difference.

By the way, the 2372B is one of those few well designed
controllers that have jumpers to enable/disable the BIOS, the
floppies, and to relocate the IO ports; I am hard pressed to
think of any other RLL controller (or MFM) that you can as
easily configure as second controller.

I will probably be switching to SCSI myself, because my main
problem is backplane slots (I made the crucial mistake of
getting a "baby AT" motherboard).
-- 
Piercarlo "Peter" Grandi           | ARPA: pcg%cs.aber.ac.uk@nsfnet-relay.ac.uk
Dept of CS, UCW Aberystwyth        | UUCP: ...!mcvax!ukc!aber-cs!pcg
Penglais, Aberystwyth SY23 3BZ, UK | INET: pcg@cs.aber.ac.uk