> > Note that only ONE computer can have ACTUAL PHYSICAL access to the
> > SCSI Disk. The other machines must have virtual access, which means
> > that one machine only does the physical I/O. This can be explained
> > as follows: Suppose you had two computers connected to the same SCSI
> > drive. Suppose one of them went to read or write from the drive and
> > found that the SCSI bus was busy. What would it do? It would reset
> > the bus and retry. The other computer would then find that its
> > I/O was aborted. It would then reset and retry. This would go on
> > "forever" even if it was a read-only device!
>
> On the contrary SCSI has full multi host/target arbitration - it depends
> on your controller how happy it is but its fine, and sharing an ext2fs
> disk Read only is just perfect
>
Not true. It depends upon the DRIVER. There isn't a driver that I've used
in Linux (or Sun) that knows what to do when some other host takes over
the bus. Try it. The first error will be the bus-phase error. The rest are
all down hill from there.
We thought it would be a real good idea to share a CD-ROM between two
Linux Boxes. After that fiasco, I tried it on my Suns. Just because
a bus Interface Specification allows any SCSI Host to be a Master, doesn't
mean that an Operating System will allow it!
We have a RAID assembly that strips SCSI drives. The SCSI I/O ports go
to a Board with a '68000 and 330 megabytes of RAM, not to the physical
drives. The 68000 is "in charge" of the drives. It is the Lock Manager.
Cheers,
Dick Johnson
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Richard B. Johnson
Project Engineer
Analogic Corporation
Voice : (508) 977-3000 ext. 3754
Fax : (508) 532-6097
Modem : (508) 977-6870
Ftp : ftp@boneserver.analogic.com
Email : rjohnson@analogic.com, johnson@analogic.com
Penguin : Linux version 2.1.29 on an i586 machine (66.15 BogoMips).
Warning : I read unsolicited mail for $350.00 per hour. Supply billing address.
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-