Persistent Reservation Proposal - Group Reservations

Knight, Frederick Frederick.Knight at
Thu Jan 3 08:33:58 PST 2008

* From the T10 Reflector (t10 at, posted by:
* "Knight, Frederick" <Frederick.Knight at>
I'm still mulling over some of these discussions, but
absolutely agree with #1 - a new reservation type is preferred.
As for #2, I disagree.	How would I remove a single initiators
registration (preempt a single initiator from the group) if they
all must have the same KEY to join the group?
More comments later.
	Fred Knight
-----Original Message-----
From: Black_David at [mailto:Black_David at] 
Sent: Thursday, January 03, 2008 9:19 AM
To: Gerry.Houlder at; t10 at
Subject: RE: Persistent Reservation Proposal - Group Reservations
* From the T10 Reflector (t10 at, posted by:
* Black_David at
I'm still checking with our implementers, but my initial reaction is
that Gerry's 2-for-2:
(1) I strongly agree with Gerry's preference for a new RESERVATION
	type over a new REGISTRATION type.  PR code is already
	subtle in a number of ways, and a new reservation type is
	much easier to isolate from existing types in specification,
	coding, and testing.  It should also have better behavior
	when mixing implementations that don't all support the
	new functionality.  We probably need two new types, one
	for group write and one for group exclusive.
(2) Is there a reason why we can't use the existing reservation
	key as the entity that has to match for the new reservation
	type?  One would have to ensure that the reservation key
	can't be read from the device by PR IN, but we already
	have the precedent (and the specification text) to do
	that in the All Registrants reservation types.	Reuse of
	the reservation key is going to be easier to cope with
	than inventing a new group identifier.
What initiator implementations are likely to use this new functionality
for what purposes?
David L. Black, Distinguished Engineer
EMC Corporation, 176 South St., Hopkinton, MA  01748
+1 (508) 293-7953	      FAX: +1 (508) 293-7786
black_david at	   Mobile: +1 (978) 394-7754
> -----Original Message-----
> From: owner-t10 at [mailto:owner-t10 at] On Behalf Of 
> Gerry.Houlder at
> Sent: Wednesday, January 02, 2008 4:40 PM
> To: t10 at
> Subject: RE: Persistent Reservation Proposal - Group Reservations
> * From the T10 Reflector (t10 at, posted by:
> * Gerry.Houlder at
> *
> So this is Roger's preference:
> >1) Define a new type of REGISTER that contains one (or more) GRIDs;
> >2) Extend RESERVE to include a single GRID, and only Initiators that
> registered (or will register) with a matching GRID get access under
> reservation;
> >3) Don't change PREEMPT, superseding reservations etc. at all - keep
> rules for handling the reservation keys completely orthogonal to the
> >4) Don't allow GRIDs to be accessed via PR In.
> If we don't add a new reservation type, it sounds like you are
describing a
> new registration type (existing one without GRID, new one with GRID).
> seems to complicate the rules for making an "all registrants"
> If the initiator making the reservation specifies a GRID, only other 
> initiators that registered with that GRID value inherit the
reservation and
> the others are excluded. This would be a very different result for
> initiators that expect to inherit any reservations just by
> Further, the "unexpectedly excluded" registered initiator will get no
> as to why it doesn't inherit the reservation. if it issues READ
> it gets back a response that says an all registrants reservation is in
> force. The PR generation and reservation key values returned won't
help any
> either, and the GROUP ID value of course will not be returned.
Creating a
> new reservation type would help here, since the reservation type is 
> returned by READ RESERVATION. This might be an advantage of creating a
> reservation type for GRID Registrants Only (or something like that).
> new reservation type would make it more obvious why you didn't inherit
> reservation you expected to inherit.
> Also for backwards compatibility, will initiators be able to register
> existing method (i.e., not specifying a GROUP ID) as well as a new
> that specifies a GROUP ID? The standard will have to describe how 
> registrants without a group ID, registrants with a non-matching group
> and registrants with a matching group ID will interact with the
> registrants only reservation and a "GRID registrants only"
> Do we really lose that much if we simply create a "matching
> key" reservation instead? That means only initiators that register
with a
> matching reservation key inherit the reservation. We lose a little bit
> security because the matching ID value is publicly reported and a
> initiator can still join, but a malicous initiator could probably get 
> around the Group ID value match just by bute force retries anyway (how
> bytes of group ID is enough?), or just preempt the group ID
reservation and
> replace it with a regular registrants only reservation. This is a
> method of creating a Group ID reservation that probably works just
fine for
> co-operating initiators (as opposed to previously described malicious 
> ones).
> *
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