Re: //gs & //e -> same HD

[toddpw@blend.ugcs.caltech.edu (Todd P. Whitesel)]

lurch@eskimo.com (Erik Kloeppel) writes:

>nope - - I'm getting ready to do this very thing with 2 IIGSs.. everybody
>I've talked to says you can NOT use teh RAMFast.  Apparently the RF does not
>support hardware arbitration.  There is some discussion as to whether the
>Apple Hi Speed SCSI card does or not.

The RAMFast and the older Mac SCSI Firmware don't arbitrate. This means that
if the other machine is using the bus when the RAMFast wants to talk it will
simply start talking and you will probably crash both machines real fast. It
has been claimed that the performance is better this way, but that is B.S. --
the arbitration time is easily dominated by the drive response time and raw
data transfer time. Host SCSI ports which don't arbitrate are just lazy.

The Hi Speed SCSI card and newer Mac SCSI Firmware _do_ arbitrate.
However this is not the comprehensive solution that many people think it is.
SCSI arbitration means that more than one device on the bus can initiate
commands without crashing the bus. It DOES NOT mean automatic disk sharing.

If you have two computers on the same SCSI bus and they both arbitrate, you
_can_ safely share read-only disk partitions. You can also share a single
disk drive as long as each host computer mounts different writable partitions.
But you cannot share writable partitions without special software. No modern
O/S that I know of contains built-in support for this kind of a setup, since
everyone assumes you will be using a network and file server machine instead.

I recall that Cirtech's SCSI card could be used to do real SCSI file sharing,
but I don't know if there was ever a GS/OS driver available that supported
it. Maybe someone else knows...

Todd Whitesel
toddpw @ ugcs.caltech.edu