Re: T10 adds locally assigned UUID designation descriptor

[Hannes Reinecke <hare@suse.de>]

On 02/08/2016 09:04 PM, Douglas Gilbert wrote:
> On 16-02-08 02:00 PM, James Bottomley wrote:
>> On Mon, 2016-02-08 at 12:33 -0500, Douglas Gilbert wrote:
>>> Recently, in draft spc5r08, T10 added a locally assigned RFC 4122
>>> UUID *** designation descriptor. That descriptor can now be
>>> returned for VPD page 0x83 (device identification) amongst others.
>>> It can be used anywhere SCSI needs a unique identifier expanding
>>> the previous set of preferred identifiers: EUI, NAA and SCSI_name
>>> (iSCSI).
>>>
>>> In the soon to be released sg3_utils version 1.42 the new UUID
>>> designation descriptor is decoded including Hannes' --export
>>> option found in sg_inq, for example:
>>>
>>> # sg_inq --export /dev/sg0
>>>     ...
>>>     SCSI_IDENT_LUN_UUID=11223344-5566-7788-aabb-ccddeeffffee
>>>
>>> Perhaps some udev work is needed to incorporate this new identifier.
>>
>> Hm, we're going to have to do this carefully.  With the move to GPT
>> partitions, both the UUID= designator in fstab and the /dev/disk/by
>> -uuid/ of udev means the GPT UUID.  In theory the design of the UUID
>> space is to allow random selection without clashing, so we could just
>> place the SCSI ones in here as well and perhaps there won't be a
>> problem, but I'd like us to think about the consequences first.
> 
> The UUID proposal (16-005r1 from Fred Knight and "Dr. Hannes Reinecke")
> was somewhat controversial with five T10 members voting against it. The
> minutes state: "The members voting no stated concern that this proposal
> may result in market confusion, and those members intend to develop
> proposals to mitigate any confusion."
> 
> Locally assigned identifiers are not new: there already is an 8 byte
> locally assigned NAA identifier (NAA=3). It is not much used, perhaps
> the new locally assigned UUID (which is 16 bytes long) will find
> more use. As for the 'sg_inq --export' naming, that seems to nail
> down the context of the new UUID pretty well:
>   SCSI_IDENT_[TARGET|PORT|LUN]_UUID
> with the identifier itself in canonical UUID format. So there should
> be no confusion there. And partitions are nested inside logical
> units and SCSI does not define those (apart from on tapes).
> 
Precisely.

These uuids will show up under /dev/disk/by-id
(as this is a hardware ID coming from the device).
So the existing UUID= or /dev/disk/by-uuid won't be influenced.
And UUID handling is confusing already (with basically every
subsystem providing one), so adding one more won't matter much :-)

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@suse.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
HRB 21284 (AG Nürnberg)
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