🚀 go-pugleaf

In article <125867@sun.Eng.Sun.COM> cramer@sun.com (Sam Cramer) writes:
>Don't Macs reserve SCSI ID 7 for themselves?  If so, it seems like having
>two SCSI devices on the bus with the same ID is a bad idea.  On the other
>hand, maybe it all works out because Macs do polled I/O, so one Mac grabs
>the bus until the SCSI command is completed.

Polling would work if the SCSIGet/SCSISelect routines would perform a Bus
Arbitration phase before blasting stuff out on the Bus.  Unfortunately, under
the current OS (6.x), they do not.  Also, I would be VERY careful if a
volume was simultaneously mounted on two systems.  The Volume Control Blocks
and allocation maps are almost certainly guaranteed to get out of Sync, since
there is no way for one Mac to tell the other that they have been changed.

One possible problem, EVEN WITH ARBITRATION, is that if both Macs tried to
select simultaneously, they could not tell who won because they both would
be setting the same selection bit (bit 7).

In general, then, this is NOT a good idea.  Keep your copy of the SUM utilities
handy.

Marc Kaufman (kaufman@Neon.stanford.edu)