Re x+1: SAM-2 Revision 11

Ralph O. Weber ralphoweber at CompuServe.COM
Sat Sep 11 21:47:32 PDT 1999


* From the T10 Reflector (t10 at t10.org), posted by:
* "Ralph O. Weber" <ralphoweber at compuserve.com>
*
Gene,

Regarding:

} Well now I thought we had made it clear that multi-ported devices 
} can have one device server implemented which (...) does the chores 
} for as many LUNs that it has hanging around.

My recollection is that we agreed to require a single set of logical
units behind the multiple ports of an SMU.  The wording representing
the agreement appears at the beginning of 4.10.1: "A single Task 
Manager and collection of Logical Units share all the SCSI Devices 
and Service Delivery ports in the SMU."

I think other parts of SAM and SAM-2 pretty clearly show the
Device Server as a component of each Logical Unit (specifically
figures 6 and 16 and the first sentence in 4.8).  I can't find
anything in the SAM or SAM-2 models that requires or prohibits 
a single Device Server per Target.

} I agree that until the Application Client peeks at the World-Wide 
} Name (not port ID) that it appears that there are a bunch of 
} Device Servers. I also agree that there could be a plethora 
} of Device Servers getting all tangled up on one piece of media.

At the risk of digging this pit even deeper, the Application
Client never has any idea how many Device Servers are out there,
the Application Client only knows how many Logical Units are
out there (with the trusty assistance of the REPORT LUNS
command).  The World-Wide Name is a piece of information
describing a Logical Unit that a Device Server returns to
an Application Client while preforming its Device Server
duties executing commands on behalf of that Logical Unit.

I take the following statement from the definition of the
Identification VPD page as showing this point of view:
"The device identification page (see table ...) provides 
the means to retrieve zero or more identification descriptors
applying to the logical unit."

By way of a somewhat weak analogy, the initiator and target 
are telephones.  The device server and application client 
are people talking on the telephones.  The phone numbers 
belong to the telephones, not the people talking on them
(regardless of how tempted we might be to think otherwise).

Thanks.

Ralph...


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