Subject: Some questions about naming (newbie)

From: "Justin R. Bendich" <[email-masked]>
Date: Wed, 18 Apr 2001 08:28:17 -0500

Hello. I'm a developer at TrelliSoft. We have a product that, among other
things, discovers the disks attached to the computer on which we run.
This information is centralized, and an attempt made to identify disks
visible from multiple computers. That's why i'm interested in the answers
to the following questions. Perhaps some of these are answered in the
draft specification, but it's a long document, so any help (including refer-
ence to specific sections of the draft) would be appreciated.

1. Can the node-name (formerly WWUID) of an iSCSI target change?
2. Can the WWN of a FC target change (sorry -- i'm not that familiar with FC)?
3. Is there any requirement/recommendation that iSCSI devices report their
   node-name in the INQUIRY return (i would suspect VPD page 0x83)?

My preferences for the answers to those questions would be:

1. No
2. No (i think that one's true)
3. Yes

and if the (naming) specification is not so evolved yet, perhaps input at
this point can still affect it?

Justin R. Bendich
TrelliSoft, inc.
(630) 545-0576 x14
[email-masked]

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From: Mark Bakke <[email-masked]>
Date: Wed, 18 Apr 2001 09:00:21 -0500

Justin-

The answers to all three questions should generally be "no".

The iSCSI node name of a target is independent of the target's
addresses, and does not change over time.  I believe the same to
be true of a FC WWN.  However, care must be taken with FC WWNs;
there are several types:

1. A Target WWPN (world-wide port name) is different for each
   interface on an FC device, and does not uniquely identify the
   target.

2. A Target WWNN (world-wide node name) is often just set to be
   the same as the port name, perhaps with a high-order bit set.
   Although I think it was intended to be a way to correlate
   different ports on the same target, I don't think that all
   implementations have done it that way, so it may not be reliable.

3. A LUN WWN is at the SCSI LUN level, and can be used for identifying
   LUNs regardless of whether the underlying transport is FC, parallel
   SCSI, or iSCSI.  However, most FC devices do not support the LUN
   WWN, and use serial numbers, device IDs, and other mechanisms to
   correlate them.  To do this, one must implement device-type-specific
   code.

Anyway, those were just a few observations that might help.

On question 3, keep in mind that an INQUIRY is done at the SCSI
level, and is independent of the SCSI transport mechanism used.
Therefore, the VPD information would not return anything that would
reflect an iSCSI identifier.  The ability to return a LUN WWN (from
(3) above) on this page really is a SCSI-level thing, and has nothing
to do with FC other than that it shares the same address format.

At any rate, in order to connect to a SCSI device via iSCSI to do
the INQUIRY, you must first log in to the target at the iSCSI level.
To do this, you would already have the iSCSI name (formerly WWUI),
so you should already have the information you need without the
inquiry data.

Please let me know if this will meet your requirements, or if you
have other naming requirements.  We will be publishing another naming
draft shortly.  The draft is very close to being finished, but we
would like to know if there are needs it does not address, or that
we need to document better.

Hope this helps,

Mark

> "Justin R. Bendich" wrote:
> 

-- 
Mark A. Bakke
Cisco Systems
[email-masked]
763.398.1054

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From: Mark Bakke <[email-masked]>
Date: Thu, 19 Apr 2001 08:48:38 -0500

Steven-

The smaller targets (such as the individual Seagate drives) do support
LUN WWN.  However, the large storage arrays do not support LUN WWN
as a way to correlate different paths to the same LU.

--
Mark

Stephen Bailey wrote:
> 
> Mark,
> 
> >    However, most FC devices do not support the LUN WWN, and use
> >    serial numbers, device IDs, and other mechanisms to correlate
> >    them.
> 
> ?
> 
> Every FC target I recall checking this on reported what looked like a
> WWN.  Some (many?) ||SCSI targets seemed to do this too.  I know other
> formats are supported, like vendor ID+serial number, but I can't
> recall seeing a target which reported ONLY this and not a WWN as well.
> Am I all wet?
> 
> Thanks,
>   Steph

-- 
Mark A. Bakke
Cisco Systems
[email-masked]
763.398.1054

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From: Stephen Bailey <[email-masked]>
Date: Thu, 19 Apr 2001 09:34:01 -0400

Mark,

?

Thanks,
  Steph