Unit Attention with multiple LUNs? -Reply

Gerry Houlder Gerry_Houlder at notes.seagate.com
Fri Nov 22 09:31:32 PST 1996

* From the SCSI Reflector (scsi at symbios.com), posted by:
* Gerry Houlder <Gerry_Houlder at notes.seagate.com>
I'll answer his easy question first:

>... it reminds me of a broader question, namely:
>why does the standard bother to minimise unit
>For example, the 6h 2Ah "mode parameters changed"
>goes only to initiators other than the one who
>dispatched the 15h/55h mode select command.

In this case, it is assumed that the initiator that sent the changed
parameter(s) knows he has changed something and doesn't
need a Unit Attention in a following command to remind it.
The other initiators, however, won't know about the change
unless a Unit Attention is created for them.

Also, there is the case of mode parameters that are saved
on a "per initiator" basis. This is allowed and some devices
actually do this. In this case a changed mode parameter
doesn't result in Unit Attention for anyone because only the
parameter for the sending initiator changed and none of
the others changed.

As for you main question, where you want a reply to the
"Unit Attentions after move media command": I've never
worked with Medium Changers (or even with multiple LUN
devices in general) so you probably know more about the
consequences of changing the medium than I do.

The rule for other initiators is clear: If one initiator does
something that another initiator should know about (to
keep him from doing something stupid) then a Unit Attn
is set for those initiators. A Unit Attention doesn't have to
be set for the initiator that did the action (devices assume
initiators know what they did).

The part that is NOT clear is whether a single event should
cause Unit Attention condition on each of several LUNs for
an initiator. If this case isn't discussed or explained in the
model for medium changers, it ought to be.
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