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

"Knight, Frederick" <Frederick.Knight@netapp.com> Tue, 02 March 2010 18:20 UTC

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Thread-Topic: [storm] SCSI Version Descriptors - iSCSI and SAM-5
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From: "Knight, Frederick" <Frederick.Knight@netapp.com>
To: <Black_David@emc.com>, <storm@ietf.org>
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Subject: Re: [storm] SCSI Version Descriptors - iSCSI and SAM-5
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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
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David L. Black, Distinguished Engineer
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