Re: Sharing SCSI disks

Leonard N. Zubkoff (
Fri, 21 Mar 1997 10:21:16 -0800

Date: Thu, 20 Mar 1997 18:48:07 -0500 (EST)
From: "Richard B. Johnson" <>

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.

Depending on the particular host adapter, this may or may not be a property of
the driver. For a BusLogic MultiMaster or Adaptec 1542C, all SCSI negotiation
is handled by the host adapter's onboard processor and its associated firmware
program. Either the firmware works correctly in a multi-initiator environment
or it doesn't, but the driver has nothing to do with it. For host adapters
like the Adaptec 7xxx or NCR/Symbios 53c8xx, the OS driver provides "scripts"
or "sequencer" code that runs on the SCSI sequencer chip, so the driver would
indeed affect whether a multi-initiator is possible. For any host adapter that
isn't completely dumb, the underlying hardware also has to work properly in the
presence of multiple initiators.

The SCSI protocols are *designed* to support multiple initiators on the same
bus. Other hosts do not "take over" the bus. They must arbitrate for control
of the bus when they wish to initiate or continue an operation.