Questions on SES specification -> Secondary subenclosures

Raj Divecha Raj.Divecha at dothill.com
Fri Dec 23 09:37:07 PST 2011


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Section 4.3.1 from SES 2r20 (as well as 3r02) working draft mentions the
following...
The primary subenclosure may access enclosure service information in a
subenclosure using the SEND
DIAGNOSTIC command and RECEIVE DIAGNOSTIC RESULTS commands over a SCSI
transport protocol,
or may use a vendor-specific interface.
This tells me that enclosure-to-enclosure communication is allowed over SCSI
transport protocol and thus I have those queries. Please readdress them.
I have an architecture that has secondary subenclosures physically inside an
enclosure. And the information between the outer enclosure and inner
enclosures would be communicated over SCSI transport protocol. The outer
enclosure may or may not have initiators but have targets with ESP. The inner
enclosures have targets with ESP and the drives. This makes the SES LU of the
inner enclosures visible to the initiator within the outer enclosure or an
external initiator. We can program the internal initiator to communicate with
the SES LU in the outer enclosure only. And we can also program the SES LU of
the outer enclosure to consolidate enclosure information from all the inner
enclosures and present it to the initiator. However, when it comes to
external initiator, we might not have control over it.
[ER] Enclosure-to-enclosure communication is vendor-specific; I2C or other
low-speed busses are candidates. They have to coordinate their IDs somehow.
[RD] If the SES LU of the inner enclosure is visible to the external
initiators and if the application client sends a RECEIVE DIAGNOSTIC RESULTS
request to the same then even if the ESP knows its subenclosure ID it cannot
report that in its diagnostic pages. I am saying this because this ESP (one
in the inner enclosures) only reports its own information, which means it
would report only one enclosure in its Configuration diagnostic page
response. And as per the SES spec, that one enclosure descriptor is for the
primary enclosure, which then has to report a subenclosure id as 0. Thus,
even if this ESP knows the subenclosure id assigned by the primary ESP, it
cannot report the same. This shouldn't create any problem in the primary ESP
as it can updated the subenclosure id fields, during consolidation, based on
where the information is coming from.
[ER] The secondary subenclosure concept is mainly for architectures that
don't provide direct access to the secondary subenclosure; if there is direct
access, then it's a primary subenclosure and need not be secondary to
another.
[RD] Based on this statement I guess I shouldn't create an SES LU in the
inner enclosure, even if it is possible. That way I won't have to worry about
direct access, correct?
From: Elliott, Robert (Server Storage) [mailto:Elliott at hp.com]
Sent: Thursday, December 22, 2011 6:10 PM
To: Raj Divecha; t10 at t10.org
Subject: RE: Questions on SES specification -> Secondary subenclosures
Enclosure-to-enclosure communication is vendor-specific; I2C or other
low-speed busses are candidates. They have to coordinate their IDs somehow.
The secondary subenclosure concept is mainly for architectures that don't
provide direct access to the secondary subenclosure; if there is direct
access, then it's a primary subenclosure and need not be secondary to
another.  A dual-domain architecture is possible where two subenclosures are
viewed as primary and secondary from one enclosure services process and
secondary and primary from the other; the ENCLOSURE LOGICAL ID will indicate
if that is the situation.
From: owner-t10 at t10.org<mailto:owner-t10 at t10.org>
[mailto:owner-t10 at t10.org]<mailto:[mailto:owner-t10 at t10.org]> On Behalf Of
Raj Divecha
Sent: Tuesday, 20 December, 2011 7:13 PM
To: t10 at t10.org<mailto:t10 at t10.org>
Subject: Questions on SES specification -> Secondary subenclosures
Hi,
I believe a secondary subenclosure can refer to...
1)	An enclosure that is physically inside a primary enclosure. and
2)	An enclosure that is physically outside a primary enclosure.
It is the primary enclosure that would assign the subenclosure identifier to
various secondary subenclosures. Is the primary enclosure required to
communicate this subenclosure id to a secondary subenclosure? If yes, what is
the recommended mechanism?
Can a secondary subenclosure also have a SES LU visible to the application
client? I assume yes, as the information can be requested using Receive
Diagnostic Results command.
If yes, and if the application client requests enclosure information directly
|from the subenclosure, then should it report subenclosure id as 0 or
non-zero? I assume it should be 0 as it is the primary enclosure for the
information it is reporting.
And, when the primary enclosure is consolidating the enclosure information
|from more than one secondary subenclosure, it will update the subenclosure id
field(s) based on where the information came from. Is this understanding
correct?
Thanks,
Raj



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