Really getting rid of AEN

Paul von Behren paul.von.behren at sun.com
Tue Jan 7 13:58:26 PST 2003


* From the T10 Reflector (t10 at t10.org), posted by:
* Paul von Behren <paul.von.behren at sun.com>
*
I don't have a problem with deprecating the current AEN text.  
I think there's a need for asynchronous events, but I realize
that it doesn't easily fit with existing SCSI architecture.
And I agree that there's no point in specifying something that
is not implemented.  Perhaps deprecating the AEN wording
will help open the door for something implementable. 

Paul

Ralph Weber wrote:
> 
> * 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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> >>
> >>
> >
> >*
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> >
> >
> >
> 
> *
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