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From: jr@frog.UUCP (John Richardson)
Newsgroups: comp.unix.i386
Subject: Re: SCSI and 386/ix
Summary: CPU moves the data
Keywords: scsi 9380s under 386/ix
Message-ID: <11826@frog.UUCP>
Date: 6 Feb 90 05:45:00 GMT
References: <1612@aber-cs.UUCP>
Organization: Charles River Data Systems
Lines: 36

In article <1612@aber-cs.UUCP>, pcg@aber-cs.UUCP (Piercarlo Grandi) writes:
> 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;
> 
   The CPU moves the data on all WD1003 compatible controllers. It uses
the INSW instruction. The AHA-1542 uses real master mode DMA to move the
data without CPU intervention.


> * you don't get scatter-gather, which is a 1542 good idea (does
> anybody apart from ISC exloit that?);
> 
  It can if you write the driver to do so. Since the CPU moves the data,
you have a programable scatter/gather mode if you do the code.

					JR