Re: SCSI URL scheme

["John Hufferd/San Jose/IBM" <hufferd@us.ibm.com>]

Right after I sent the attached, I thought of another reason that folks
might me having a problem here, and that is, they might think that the
Report Luns reports all the LUNS that are within the Storage Controller.
As I understand it, this is not the case, but it only reports the LUs that
are authorized to be seen by the questioning Host/Initiator.

.
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John L. Hufferd



John Hufferd/San Jose/IBM@IBMUS@ece.cmu.edu on 10/03/2000 12:19:19 PM

Sent by:  owner-ips@ece.cmu.edu


To:   ips@ece.cmu.edu
cc:
Subject:  Re: SCSI URL scheme



OK, now I am missing something here.

The note below seems to be talking about a Host trying to find a LU and
Raghavendra suggest that it is a big effort to do the normal Report Luns
and Inquiry.

First off, this is suppose to be done (normally) once, but perhaps at
various (logical) Plug & Play  points.  If we are talking about the Plug &
Play points in time, then there could be some additional conversation.  But
independent of that, which so far I think we have been, the Host determines
ALL his addressable LUs when he comes up, and today that means "REPORT
LUNS", followed by approprate INQUIRYs.  This is not a big deal at bring
up.

I have not followed the turn in the road that would have a Host that should
know what is connected to it (and its WWN), needing to find the WWN at some
other time.

Now it is possible that we are somehow talking about something that is akin
to the NAS approach to "Mount" (Or Drive Map).  In this mode I expect that
the Client Host has been given some Name that needs to get resolved to an
LU, or Set of LUs.  But even in that case, if the name get resolved so that
it targets a given IP Storage Device (Storage Controller), it also should
perform a Login, and then it can still perform the normal REPORT LUNs and
an approprate Inquiry.   In most cases for Desktop systems this should be 1
LU, probably the LU0.  But in any event I do not see the problem.  The
Biggest problem the Host might find is if the information found in the VPD
reported by the Storage Controller differs from what is expected. (They
call this an administrative error and needs to get fixed by people.)

In any event I do not see the value add for the Name to go all the way down
to the LU.  In fact if does not we can use the normal network processes to
connect a Client Host to the approprate Target Storage Controller.

Third party commands, however, seem to be a different set of discussion
items, so perhaps it would make since to focus on that area where it is not
clear what the approach is, rather then work areas that have a technique
that (IMHO) work OK.

And it might be valuable to discuss the issue of Plug & Play, and how that
is affected.  (By Plug and Play I mean the process of adding a new LU or
taking an LU away while every thing else continues.)

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.
.
John L. Hufferd



Raghavendra Rao <jpr@divyaroot.India.Sun.COM>@ece.cmu.edu on 10/03/2000
10:55:41 AM

Please respond to Raghavendra Rao <jpr@divyaroot.India.Sun.COM>

Sent by:  owner-ips@ece.cmu.edu


To:   ips@ece.cmu.edu
cc:
Subject:  Re: SCSI URL scheme [WAS: Re: iSCSI: 2.2.6. Naming & mapping]




> out-of-band).  I don't see the point of the initiator sending its "view"
to
> the target at any point.  If the initiator sends an incorrect view,
you've
> just created an error scenario which needs additional definition.

Well, to extend what Julian said further, the initiator could ask the
target
for a LUN value corresponding to a WWN as part of the authentication
process,
instead of presenting its view - whether right or wrong. But something like
this needs to be done as there is no easier/faster way to translate a LU
WWN
to a LUN value.

This may also help in building an authentication method for a LU access
where
no such thing exists today ?


> case, the target will send its "view" for that initiator in REPORT LUNS
> SCSI command after login (which is actually the layer that cares about
the
> LUN Map at all anyway).
>

This will be a problem if the storage controller has a lot of LUNs. Since
REPORT LUNS only returns a list of LUNs, the initiator still has to send an
INQUIRY (page 83) request to each LU to to find a matching LU WWN (or until
a matching WWN is found).

-JP