Reserve and Release for pri

Smith, Greg GREGS at
Mon Jan 15 13:09:18 PST 1996

* From the SCSI Reflector, posted by:
* <"Smith, Greg" <GREGS at>>
>          I propose that reserve and release (ordinary, SCSI-2 style,
>          not persistent and no extents) be mandatory for SCSI-3
>          printers and communications devices.
>          Both of these device models are part of the stream class of
>          devices which have an implicit state based on previous
>          commands.  To allow proper control of these devices in
>          multi-initiator environments, reserve and release are
>          required.  Therefore, I believe that these commands should
>          be mandatory.

It is possible for a printer device to maintain
multiple states (per initiator) to get around this problem. Concurrent
PostScript jobs could be run on behalf of different initiators, for 
Obviously, I don't want my 20 pages intermixed with someone else's; this
could be solved by appropriate buffering in the pre- or post-rendering
phase of the operation. When buffers become full, write commands could
be rejected. Many large Postscript film printers have hard disks in them.

Even if the printer designer expects RESERVE UNIT  to be used by the host 
prevent conflicts, the printer should be sensitive to what state was 
by what initiator. For a postscript printer, this may mean generating a 
status on all other initiators while running a postscript job for a
given initiator.

Likewise, for communications devices, if the communication protocol in
question supports concurrent independent channels there is no reason why
different initiators cannot use it concurrently.

So, I say, the reserve unit should not be mandatory; at least, the 
argument that
proper control of these devices *requires* it does not hold, from what I 

Gregory Smith               |       PH: (905) 475-1077 x 204
Legacy Storage Systems      |      FAX: (905) 475-1088
43 Riviera Drive            | 
Markham, ON Canada L3R 5J6  | INTERNET: GREGS at

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