Really getting rid of AEN

Ralph Weber ralphoweber at compuserve.com
Tue Jan 7 13:36:22 PST 2003


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

At a very fundamental level, SAM assumes that initiators
initiate transactions and targets respond to them. SAM has
zero ability to define a transaction that is initiated by
a target. May SCSI protocols take advantage of this model.

The most SAM has to offer in the way of a backwards
transaction is an event signal (see clause 6 in SAM-3 r04)
and that is a relatively new addition to SAM.

When the SAS folks tried to ram their round-peg AEN
design into the square-hole restrictions of SAM, it
became clear to all in the room that SCSI as we understand
it is not ready architecturally for AEN.

As Gerry notes, the mess associated with AEN has worked
against its implementation for over a decade. As you
note, the problems with AEN are sufficiently daunting
that implementors find any other available solution
preferable.

Perhaps, as you suggest, an equivalent to AEN would be
desirable. But, it will take someone (or a group of
someones) with a very high degree of determination to
define it, since the barriers erected by the current
SCSI model are monumental.

Regards.

.Ralph

Paul von Behren wrote:

>* From the T10 Reflector (t10 at t10.org), posted by:
>* Paul von Behren <paul.von.behren at sun.com>
>*
>But FC RAID implmentations often use LIP or RSCN for asynchronous event
>notification (e.g. LUN masking config changes).  This seems pretty
>sub-optimal, FC should not be dealing with LUNs at all.  And
>an FC-specific approach can't be extended to other transports.
>
>Seems like there's a need for some type of SCSI asynchronous event 
>notification, but perhaps not the one currently in SAM.
>
>Paul
>
>Gerry.Houlder at seagate.com wrote:
>  
>
>>* From the T10 Reflector (t10 at t10.org), posted by:
>>* Gerry.Houlder at seagate.com
>>*
>>
>>Jim, you are beating a dead horse.
>>
>>The decison to remove AEN was based on having zero implementations of AEN
>>being supported by both initiator and target in any system known to T10
>>members over the last 15 years. Further, no T10 members thought they would
>>implement AEN in the future. Even new protocols being brought into the SCSI
>>fold (SAS, Infiniband, etc.) did not foresee any need for AEN and rebelled
>>against providing an awkward (but implementable) method of doing AEN just
>>to satisfy SAM when no one would actually implement it (because it was so
>>awkward). T10 has removed other useless (at least in hindsight) features
>>with far less evidence and passage of time than this.
>>
>>
>>                    JimMcGrath at oa
>>                    ktech.com            To:     roweber at acm.org
>>                    Sent by:             cc:     owner-t10 at t10.org, T10 at t10.org
>>                    owner-t10 at t10        Subject:     Re: Really getting rid of AEN
>>                    .org
>>                    No Phone Info
>>                    Available
>>
>>                    01/06/2003
>>                    05:42 PM
>>
>>
>>
>>* From the T10 Reflector (t10 at t10.org), posted by:
>>* JimMcGrath at oaktech.com
>>*
>>
>>Ralph,
>>
>>What is suppose to replace AEN (aka AER) going forward?  That is, how does
>>a target (device server) notify the initiator (application client) of a
>>change in status unrelated to a command, and especially without awaiting
>>for a command?
>>
>>This capability is not physical protocol related, and I don't think is
>>device type related, and so should be in SAM (if not, then what document
>>will it be in?)
>>
>>Jim
>>
>>PS while I saw the notice of the decision (and vote) to remove AEN in the
>>minutes, I did not see a proposal on the topic (which would usually address
>>these sorts of issues).
>>
>>                      Ralph Weber
>>                      <ralphoweber at comp        To:       "T10, Reflector"
>><T10 at t10.org>
>>                      userve.com>              cc:
>>                      Sent by:                 Subject:  Really getting rid
>>of AEN
>>                      owner-t10 at t10.org
>>
>>                      01/06/2003 06:23
>>                      AM
>>                      Please respond to
>>                      roweber
>>
>>* From the T10 Reflector (t10 at t10.org), posted by:
>>* Ralph Weber <ralphoweber at compuserve.com>
>>*
>>In November, T10 remove AEN [aka AER] from SAM-3.
>>Now, the time has come for the other shoe to drop.
>>
>>The really (shall we say) 'interesting' work for
>>removing AEN is in SPC-3 and a proposal to do the
>>deed is available as:
>>
>>  ftp://ftp.t10.org/t10/document.03/03-051r0.pdf
>>
>>There are little bits here and there that need to
>>be removed or made obsolete, but there are two
>>areas where substantial changes are proposed:
>>
>>  - The Control mode page, and
>>  - The processor command set.
>>
>>Enjoy.
>>
>>.Ralph
>>
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>>
>
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>  
>


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