FW: RE: Question on Scope: 8-byte vs 2-byte LUNs

George Penokie gop at us.ibm.com
Mon Apr 6 07:09:54 PDT 1998


* From the T10 (formerly SCSI) Reflector (t10 at symbios.com), posted by:
* George Penokie <gop at us.ibm.com>
*
George,
I finally understand your issue and there is a solution. I should have been
more careful in my original tutorial but the new version (attached) covers all
(I think) of the issues you and I have discussed over the last few weeks. As a
result the 'mini' has gone out of the title as it is now 40+ pages long. But I
am getting ahead of myself. I would like to make sure I have solutions you
agree with. So onward.
(I will post your message and this response on the reflector just so people how
are interested can keep up with the discussion.)

2- You are correct there is no mechanism to force or not force a SCSI device to
allow or disallow access to logical units. It is implementation specific.
I agree your example is a good one (in fact I have added it to the tutorial;
hope you don't mind) and it is allowed under the current rules.

c) OK I agree - Again I was loose with my terminology and only thinking of a
system configured with one SCC per level which is, as you have pointed out, not
the only way to do things.

I think the rest of the issues fall under the 'addressing with multiple SCCs
devices under another SCC device' issue - My mistake was going down the path
that uses the REPORT LUNs command information to determine the 2-byte addresses
for used in the configuration commands. As you have pointed out this can result
in multiple virtual logical units with the same LUN which makes it impossible
to configure those virtual logical units into another virtual logical unit.
What I should have said is do not use the REPORT LUN command to determine the
two-byte LUNs use the REPORT PERIPHERAL DEVICE service action to determine
them. That service action was design to return all the peripheral devices
2-byte LUN that can be used to configure SCC devices. The REPORT LUNs command,
on the other hand, was designed to list the addresses of SCSI devices that
commands can be send to.  If the REPORT PERIPHERAL DEVICE service action is
used them the 2-byte address scheme works for your example (which I have also
included in the tutorial).

So look over the revised tutorial and see if it describes a solution you can
accept. The ball is back in your court. I'll be waiting for your response.

(For those of you who have received the tutorial I have sent you the new
version if you do not receive the new version in a day or so let me know.
Please get rid of the old one. And stay tuned I am not sure it is done yet.)

Bye for now,
George
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