SAM-2 Revision 11

Ralph Weber ralphoweber at CompuServe.COM
Thu Sep 9 14:09:45 PDT 1999


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

} -----------------------------------------------------------------
} GME:
} Logical Unit has exactly one Device Server
} Device Server is a Processing Element   (missing from table)
}
} Not clear from the document whether:
}         Device Server is part of exactly one Logical Unit
} or
}         Device Server is associated with zero or more Logical Units
} -------------------------------------------------------------------------

I've long been of the impression that figures 6 and 16 and the first
sentence in 4.8 are pretty clear on this point (revision 11).  A basic
Logical Unit is composed of ... a Device Server ... and other stuff.
How the Device Servers within several Logical Units is beyond the scope
of the model.

The requirements of the model neither force the Device Servers within
several Logical Units to interact with each other nor oblige them to
ignore each other.  As far as I can tell, this is adequate because the
single Task Manager is common to all Logical Units and is charged with
those functions that the model requires to be coordinated among the
several Logical Units.

Of course, the needs of an individual implementation might either
require the Device Servers to interact or prohibit them for interacting
in any way.  But, since the proper definition and operation of the
model have no such requirements, it is appropriate for the model
to keep a minimum scope, which allows the maximum implementation
flexibility.

} The mapping between SMU Logical Units and Logical Units is defined
} by SAM2.11 to be Vendor Unique.

Actually, SAM-2 revision 11 is silent on this topic.  (Silence does
not equate to any specific definition.)  The silence is related to
the fact that SAM-2 revision 11 is a working draft (and not even a T10
adopted working draft at that).  George Penokie has expressed concerns
that SAM-2 should not be silent on the topic of how Logical Units are
identified by Logical Unit Numbers by the several SCSI Devices in an SMU.
Although no proposals have yet been made to elucidate this topic, there
is much time between now and when SAM-2 becomes a dpANS during which such
proposals can be brought forward.

Thanks.

Ralph...




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