text of document 98-187r0

[Gerry_Houlder at notes.seagate.com]

* From the T10 (formerly SCSI) Reflector (t10 at symbios.com), posted by:
* Gerry_Houlder at notes.seagate.com
*
This proposal will be presented at the July SCSI working group meeting.=

Anyone with comments is invited to reply to me directly or to the refle=
ctor
before the meeting.

Date:     June 19, 1998
To:  T10 Committee
From:     Gerry Houlder, Seagate Technology
Subj:     Considerations for mode pages common to several LUNs

This proposal is an artifact of a previous proposal that created Mode P=
age
19h. This mode page is described in documents 96-195r4 and 98-106r1.
Discussion of these proposals brought out the fact that mode pages are
associated with Logical Unit Numbers (LUNs), not targets. However the
interface functions controlled by mode page 19h are actually associated=

with the target in this case. It is undesirable (and not feasible) to h=
ave
different settings for different LUNs, so a practical implementation wi=
ll
use the same mode page for all attached LUNs.

The existing wording for MODE SELECT command doesn?t describe how to re=
port
unit attention for a page that is common across multiple LUNs. The exis=
ting
wording from SPC-2 reads as follows:

<start quote from SPC-2>
If a target supports saved pages, it may save only one copy of the page=
 for
each logical unit and have it apply to all initiators, or it may save
separate copies for each initiator for each logical unit. Multiple port=

implementations may save one copy per logical unit and have it apply to=
 all
initiators on all ports or save a separate copy per logical unit for ea=
ch
initiator on each port. If separate copies are saved, the target shall
maintain separate current values for each combination of initiator and
logical unit that it detects. Pages that are common to all initiators a=
re
not required to have multiple copies.

If an application client sends a MODE SELECT command that changes any
parameters applying to other initiators, the device server shall genera=
te a
unit attention condition for all initiators except the one that issued =
the
MODE SELECT command (see SAM). The device server shall set the addition=
al
sense code to MODE PARAMETERS CHANGED.
<end quote>

I propose adding wording to specifically mention that a mode page may b=
e
common across multiple LUNs. When the page is changed by an initiator, =
the
device server for other LUNs that use the same page will not generate u=
nit
attention for that initiator. I believe the extra unit attentions for t=
his
case are unnecessary and don?t serve a useful purpose. This is similar =
to
the  behavior of a target with a single LUN.

If the mode page is common across multiple LUNs and is also common acro=
ss
all initiators, then the device server shall generate one unit attentio=
n
for each of the other initiators when they access that target. The othe=
r
initiators will receive unit attention the first time they access any L=
UN
on that target and won?t receive additional unit attentions when they
access another LUN on that target. Again, this is like the behavior of =
a
target with a single LUN.

My proposed wording to describe this case (which would replace the two
paragraphs from SPC-2 quoted above) is as follows:

If a target supports saved pages, it may
(a)  save one common copy of the page for each logical unit and have it=

apply to all initiators,
(b)  save separate copies for each initiator for each logical unit,
(c)  save one common copy of the page for all attached logical units an=
d
have it apply to all initiators,
(d)  save separate copies for each initiator and each copy is common to=
 all
logical units.

A target may save some pages that use a common copy for all initiators =
and
some pages that have a separate copy for each initiator. Multiple port
implementations that do options (a) or (c) shall apply the common copy =
of
the mode page to all initiators on all ports. Multiple port implementat=
ions
that do options (b) or (d) shall save separate copies for each initiato=
r on
each port.

If an application client sends a MODE SELECT command that changes any
parameters applying to other initiators, the device server shall genera=
te a
unit attention condition for all initiators except the one that issued =
the
MODE SELECT command (see SAM). If a mode page is common across all atta=
ched
LUNs, the device server shall generate a unit attention for the first
access to any attached LUN; subsequent accesses to other attached LUNs =
by
the same initiator shall not result in additional unit attention
conditions. The device server shall set the additional sense bytes to M=
ODE
PARAMETERS CHANGED.
=


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