iSCSI: T10 meeting

[Black_David@emc.com]

I spent today at the T10 meeting, despite United Airlines'
best attempts to keep me out of the Pacific time zone :-).
I did quite a bit of explaining about IETF and ips
logistics, procedures, and status, but did manage
to squeeze in some technical discussion.  

Here are a few items of relevance to iSCSI:

- As indicated earlier, T10 would like to see iSCSI
(and other encapsulations of SCSI) follow the data
formats used by FCP to the extent possible and
reasonable.  Departures for good functional reasons
are ok (e.g., iSCSI separates out task management
in a way that FCP does not, and there may be good
reasons to do that), even though they complicate
bridges.  OTOH, format differences that lack a
functional reason should be avoided.  The recent
proposal by Charles Monia to harmonize iSCSI and
FCP packet formats deserves serious attention.

- There has been some discussion of stateless bridges
or gateways on this list in the past.  T10's view of
this area is that such devices tend to be inherently
stateful because they usually have to keep state
related to proxying multiple initiators accessing them
onto a single initiator that accesses the actual
target.  Mapping command tags as part of this is not
a big deal, and hence T10 does not attempt to mandate
a single SCSI tag format -- in fact a 64 bit tag for
SCSI over VI was recommended as part of today's meeting.
The rationale for that tag may be worth considering for
iSCSI - an initiator running a 64 bit OS can stick a
memory address in the tag, which makes it easier to
handle responses.  In any case, it's not important
to match FCP's tag structure exactly.

- I want to reinforce Steve Byan's earlier email on
multiple ordered commands and resource exhaustion.
As indicated by words in our (still draft) charter,
this sort of issue expressible entirely in SCSI
w/o reference to TCP or any other transport is in
T10's domain.  That means that not only is it T10's
responsibility to deal with this issue, it is also
T10's responsibility to determine whether the issue
is serious enough to merit any changes.  This IETF
WG should be cautious about redesigning things like
ACA - it would be undesirable for ACA to behave
differently in iSCSI than in other SCSI transports.
  
From my viewpoint, a good working relationship
with T10 is well underway.

--David

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David L. Black, Senior Technologist
EMC Corporation, 42 South St., Hopkinton, MA  01748
+1 (508) 435-1000 x75140     FAX: +1 (508) 497-8500
black_david@emc.com       Mobile: +1 (978) 394-7754
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