"Tim Larkins \(EUKSHEL1PO\)" <[EMAIL PROTECTED]> wrote:
> I'm thinking of changing my Host Adapters SCSI ID to ID 15 so that I
> can free up SCSI ID 7 for use by another device.. will this cause problems
> under Linux? Will I need to make any changes/ re-install or will it happily
> cope with the ID change...
If you set the host adapter ID above 7, it might not be able to talk to
narrow devices at all. If it can talk to them, they won't be able to
disconnect (i.e., during seeks), so performance will be reduced. This is
because of the way that SCSI initiators address targets. During the
Selection and Reselection phases of a SCSI transaction, the initiator drives
the SCSI data lines corresponding to its own ID and the target ID. If the
host is at ID 8 through 15, a narrow target won't be able to tell which ID
the initiator is using.
I wouldn't do it. Get yourself a dual-port SCSI card. I've had good luck
with the Buslogic (Mylex) Flashpoint-DW and the Diamond Fireport 40 Dual.
In general, whereever possible I recommend using multiple SCSI chains instead
of trying to load everying on one. There are performance advantages to
separating slow and fast devices, and to separating devices by functionality.
For instance, it is good to have a scanner or a CDR drive on a separate chain
from your disk drives, so that you can overlap I/O when using them.
Also, even though it is possible to mix internal and external devices on
a single chain, there tends to be an impedance mismatch between internal and
external cabling. This can result in reduced reliability. I recommend
putting internal and external SCSI devices on separate controllers. Where
that isn't possible, try to minimize the number of devices and cable length
of one 'side' of the chain.
Fast SCSI is less tolerant of cabling quality issues than 'Slow' SCSI, and
Ultra is less tolerant yet. I'm not sure about Ultra2, but since it uses
differential signalling it may actually be more robust.
Cheers,
Eric
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