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

[dempson@actrix.gen.nz (David Empson)]

In article <34afl5$ofc@carroll1.cc.edu>,
Ron Higgins <rhiggins@carroll1.cc.edu> wrote:
> I've got an Apple //e connected to a Maxtor 200meg Hard Drive via a
> RamFast with v2.? ROM.  I run my BBS on this system.
> 
> I wish to keep the BBS on the //e, but would like to access the 200meg
> Hard Drive from the Apple //gs.  Presently the //gs has an Apple Rev.C
> SCSI card in it.  If I were to replace it with another RamFast, could I
> access the 200megger from the //gs?

Not with RamFasts.  The RamFast doesn't support SCSI Arbitration (i.e.
multiple "initiators" on the SCSI bus).  At the very least, this means
the two computers will "collide" if they both want to access the hard
drive at the same time.  It could cause data corruption and other
nasty side effects.

It might be possible to do this if both computers were using an Apple
SCSI card.  I _think_ the high-speed SCSI card supports arbitration.
I've never tried it, and I can't spot anything definite in the manual
(it describes the arbitration phase, but doesn't say if it implements
it properly).

However, even if the two computers can succesfully negotiate who is
going to get access to the bus, there is still the problem of
simultaneous access to the file system.

If both computers are accessign a read-only file system (especially a
CD-ROM), there is no problem.  If one is only reading and the other is
reading and writing, there are likely to be some problems - the first
computer may try to read data which has been partially updated by the
second computer, and get confused (e.g. reading from a file which is
in the process of being updated).

Writing from both computers is a definite no-no.  You will end up with
cross linked files, damaged directories, etc.

Note: if each computer is writing only to its own private partition,
and not to the partition "belonging to" the other computer, it should
be OK.

> I seem to recall that you could do it with the old CMS SCSI cards where
> you could set the SCSI ID of the computer (or host) system.

Heh heh.  I remember a situation that happened a few years ago with a
fellow IIgs owner.  He had several IIgses using CMS SCSI cards, all
linked to the same SCSI bus.  He decided to ignore the warnings in the
manual about not attempting to write to the same partition from
multiple computers.  A few weeks later he started complaining that his
AppleWorks spreadsheets started having filenames appearing in strange
places inside them, and data was being lost.

Subdirectories written by one computer were overwriting files being
saved (at the same time) by the other computer.  Boy was this a mess!

In short: you can't do this with RamFASTs.  You might be able to with
Apple cards, as long as you obey very strict rules about writing.
-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand