Re: [storm] SCSI Version Descriptors - iSCSI and SAM-5

"Mallikarjun Chadalapaka" <cbm@chadalapaka.com> Mon, 08 March 2010 07:05 UTC

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From: "Mallikarjun Chadalapaka" <cbm@chadalapaka.com>
To: "'Knight, Frederick'" <Frederick.Knight@netapp.com>, <Black_David@emc.com>, <storm@ietf.org>
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Date: Sun, 7 Mar 2010 23:05:49 -0800
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Subject: Re: [storm] SCSI Version Descriptors - iSCSI and SAM-5
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Agreed on the SAM-5 version descriptor.  I assume the new draft will in
addition reference SAM-4.

On the iSCSI version descriptions, I actually think creating a 3720+5048
version descriptor is a good start.  As Fred says, existing implementations
will be initially not reporting this so the initiator is left to other means
to figure out the compliance level (and iSCSI provides the hooks to discern
that).  However, I believe this new version descriptor will help provide
clarity down the road as existing implementations catch up to the standard -
as opposed to leaving it open-ended until all implementations catch up to
the SAM-5 draft (which takes even longer to get to).

So I guess my preference is to create a 3720+5048 version descriptor,
assuming it's OK to approach T10 any time in future with a request to add
additional milestones based on implementation feedback from the WG.

Thanks.

Mallikarjun



> -----Original Message-----
> From: storm-bounces@ietf.org [mailto:storm-bounces@ietf.org] On Behalf Of
> Knight, Frederick
> Sent: Tuesday, March 02, 2010 10:20 AM
> To: Black_David@emc.com; storm@ietf.org
> Subject: Re: [storm] SCSI Version Descriptors - iSCSI and SAM-5
> 
> I agree, we need to request a frozen SAM-5 version descriptor, and see
what
> they say.
> 
> I'm reluctant to create a new descriptor to indicate compliance with
something
> old (3720+5048).
> 
> All those existing implementations that support 3720+5048 will NOT have
that
> descriptor.  What is an initiator to think?  How will the initiator tell
an
> old compliant device that supports 3720+5048 with no descriptor from the
new
> compliant device that supports 3720+5048 but has the descriptor?  My fear
is a
> host that assumes that if the 3720+5048 descriptor you propose is NOT
present,
> then the device must NOT be 3720+5048 compliant.
> 
> I'm reluctant to punish existing compliant devices by creating a
descriptor
> that they will not report.  The horse is already out of the barn, what
good
> will it do to post a "please close the door" sign?
> 
> We should however, request that T10 create a descriptor that indicates
> compliance with the new SAM features draft (which therefore means
> 3720+5048+xxx; where xxx=the new SAM features RFC).  If the device doesn't
> report this new descriptor, then you must use iSCSI mechanisms to
determine if
> the device is 3720 only, or 3720+5048.
> 
> 	Fred Knight
> 
> -----Original Message-----
> From: Black_David@emc.com [mailto:Black_David@emc.com]
> Sent: Monday, March 01, 2010 5:53 PM
> To: storm@ietf.org
> Subject: [storm] SCSI Version Descriptors - iSCSI and SAM-5
> 
> <WG Chair Hat On>
> 
> We have some interesting technical decisions to make around asking for
some
> SCSI version descriptor values.  For those not familiar with them, a SCSI
> device can return up to 8 2-byte version descriptors in bytes 58-73 of
> standard INQUIRY data (see section 6.4.2 in SPC-3 or the latest draft of
SPC-
> 4).  A version descriptor value specifies both a standard and a revision.
> Version descriptor values are defined by explicit action at T10; this
serves
> as an indirect control over which versions of standards to which a device
can
> claim to comply, and discourages compliance with revisions that are
unstable
> or otherwise unsuitable.  T10 only assigns version descriptors to drafts
of
> standards that T10 believes to be stable (e.g., suitable to implement
from).
> 
> The straightforward decision is that the iSCSI features update draft
(draft-
> ietf-storm-iscsi-sam) will need to reference a stable version of the SAM-5
> standard (under development) prior to the completion of SAM-5 work at T10.
I
> suggest that Fred Knight (editor of the draft) and I discuss this at next
> week's meeting of T10 (specifically, the CAP WG in T10) in a couple of
weeks
> and bring the resulting recommendation to the storm WG list and the
Anaheim
> meeting.  Based on what's in the current draft of SAM-5, T10 may assign a
> version descriptor, or recommend that we wait for some more things that
are
> known to be inbound.
> 
> The more interesting decision is version descriptors for iSCSI.
Currently,
> there's only a generic version descriptor value , 0x960h "iSCSI (no
version
> claimed)".  There are an additional 31 descriptor values available to
iSCSI,
> and so the question to the storm WG is - what would we like to see
defined?
> 
> I have two initial suggestions:
> 1) I suggest asking that a version descriptor be defined for the
combination
> 	of RFC 3720 (iSCSI) and RFC 5048 (iSCSI corrections and
clarifications)
> 	to enable a device to claim that it has implemented RFC 5048.  We
could
> 	add additional RFCs to this set, e.g., RFC 3980 for NAA names,
although
> 	I'm not sure that's useful to know post-login.'
> 2) I strongly suggest *not* asking that a version descriptor be defined
> 	for RFC 3720 by itself, as I'm concerned that such a descriptor
would
> 	serve as a (small) disincentive to implement RFC 5048.
> Please comment on these.
> 
> Thanks,
> --David
> ----------------------------------------------------
> David L. Black, Distinguished Engineer
> EMC Corporation, 176 South St., Hopkinton, MA  01748
> +1 (508) 293-7953             FAX: +1 (508) 293-7786
> black_david@emc.com        Mobile: +1 (978) 394-7754
> ----------------------------------------------------
> 
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