Doubts in SBP2 Spec/draft Revision 4 - URGENT

PJohansson at aol.com PJohansson at aol.com
Wed Sep 1 09:59:16 PDT 1999


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* PJohansson at aol.com
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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.

<<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.

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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