Doubts in SBP2 Spec/draft Revision 4 - URGENT

Nagaraj G gnagaraj at wipinfo.soft.net
Wed Sep 1 19:18:21 PDT 1999


* From the T10 Reflector (t10 at t10.org), posted by:
* "Nagaraj G" <gnagaraj at wipinfo.soft.net>
*
Thanks Peter for the reply,

My comments on your answers embedded. Pls. reply.


-----Original Message-----
From: owner-t10 at t10.org [mailto:owner-t10 at t10.org]On Behalf Of
PJohansson at aol.com
Sent: Wednesday, September 01, 1999 10:29 PM
To: T10 at t10.org
Subject: Re: Doubts in SBP2 Spec/draft Revision 4 - URGENT


* From the T10 Reflector (t10 at t10.org), posted by:
* PJohansson at aol.com
*
In a message dated 99-09-01 10:39:11 EDT, gnagaraj at wipinfo.soft.net writes:

<<The LUN (Logical Unit Number) is a 16 bit field in the spec/draft.
(section
7.4.11 and section 5.1.3.1)

My question is: should this LUN be adapter-wise or system-wise. i.e., if
there are two(or more) adapters in a system and each adapter has Logical
units connected to them, then should the LUNs be numbered from zero on each
adapter or should they be numbered in sequence. I mean, if, for example, I
have 2 adapters and two logical units in each adapter, then should the LUNs
be numbered 0 & 1 in each or should they be numbered 0,1,2 & 3.>>

PGJ: The LUN is a property of the device (target), not the adapter
(initiator). When you say you have two logical units in each adapter, it is
confusing. Are you planning adapters that ALSO have target capability? In
this case, their logical unit numbers may be whatever you like, including
LUN
0 and 1 in adapter A and LUN 0 and 1 in adapter B. The numbering of LUNs in
one target is not related to another.

::::GNR:::: Assuming the case of one device having two adapters (two serial
bus paths), both are SBP2 target capable and each is connected to two
logical units. If the LUNs are numbered in the above said way, and since the
Config ROMs of both the nodes (targets) have the same Unit_Unique_ID as per
sec 7.4.12 and 7.6 the Initiator detects these two nodes(targets) as one
target device. Now if the LUNs are numbered in the above said way, they
should be numbered that way in the Config ROMs of each adapter. In this
case, how should the initiator identify the LUNs on the target? The
Initiator is identifying the targets as a single unit having two serial bus
access paths by the Unit_Unique_ID. Now, if the initiator has to login to
the Logical units on this unit having two serial bus access paths and having
LUNs separately in each access path, how should it specify the LUN to login?


<<Please clarify the sections 7.4.12 and 7.6.

My doubt is: in sec 7.4.12  the draft says

"The Unit_Unique_ID entry is an optional leaf entry in the unit directory
that describes the location of the unit unique ID leaf within configuration
ROM. If a vendor implements a device with multiple Serial Bus access paths,
i.e., multiple links to Serial Bus each of which receives a distinct node_ID
as the result of Serial Bus initialization or bus enumeration, the
Unit_Unique_ID entry shall be implemented."

and in sec 7.6 it says

"Although the node unique ID (EUI-64) present in the bus information block
is
sufficient to uniquely identify nodes attached to Serial Bus, it is
insufficient to identify a target when a vendor implements a device with
multiple Serial Bus node connections. In this case initiator software
requires information by which a particular target may be uniquely
identified,
regardless of the Serial Bus access path used"

If this is the specification to have a target with multiple adapters
(multiple paths), then how should the LUNs be identified. If the initiator
identifies the target by this "Unit Unique ID" and accesses the Logical
Units
on the target, then it requires the LUNs to be numbered in sequence at the
target even if it has multiple adapters and each connected to different
Logical Units. If this is the case, then how should one implement SCSI
devices (Logical Units) which support only three bits of LUN field? Should
there be a mapping at the target for all these cases?>>>

PGJ: The problem with multiple interfaces to Serial Bus is that each one (a
node) presents its own unique ID, EUI-64. If two nodes are, in fact,
different ports to the same device, how can one determine this? At first
glance they appear to be different devices; one doesn't even know that these
nodes exist within the same physical enclosure. The solution is to give each
device (unit architecture / unit directory) a different 64-bit identifier,
Unit_Unique_ID, and make sure they are the SAME for all access paths (nodes)
that connect to the same device.

HINT: Each access path (node) has separate configuration ROM.

::::GNR:::: If the Initiator identifies the target as a single device having
two serial bus access paths, how should it identify the Logical Units on
each access path?


Regards,

Peter Johansson

Congruent Software, Inc.
98 Colorado Avenue
Berkeley, CA  94707

(510) 527-3926
(510) 527-3856 FAX

pjohansson at aol.com
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Regards,

Nagaraj

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