SCSI and 386/ix

John Richardson jr at frog.UUCP
Tue Feb 6 16:45:00 AEST 1990

In article <1612 at aber-cs.UUCP>, pcg at aber-cs.UUCP (Piercarlo Grandi) writes:
> In article <25c77e8b:490.5comp.unix.i386;1 at nstar.UUCP>
> larry at 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.


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