Really getting rid of AEN

JimMcGrath at oaktech.com JimMcGrath at oaktech.com
Tue Jan 7 13:16:01 PST 2003


* From the T10 Reflector (t10 at t10.org), posted by:
* JimMcGrath at oaktech.com
*






Paul,

My point exactly.  Up until now the AEN feature of SAM has provided a
"cover" for SCSI on this issue, even if it was a poor one.  I agree with
Gerry than AEN was not widely implemented.  But its proposed removal opens
up the issue of how to cover asynchronous state changes.

Note that specific protocols may have some differences in implementation to
address this issue.  This is true for other features of SAM as well.
Afterall, LUNs are expressed and transferred in very different ways in many
protocols, but can all be mapped to the SAM concept of LUNs.

I propose that any proposal to remove a feature look at the impact of the
removal - and propose either doing away with the capability entirely or
addressing it in some other way.   Part of my issue here is that I'm not
sure what T10 was discussing - the AEN implementation or the architectural
need to address the issue of asynchronous status changes.  That is why this
sort of thing in best done in a proposal, not noted in a couple of
sentences in the T10 minutes.

Personally, since RAID systems and any system using removable media
encounter asynchronous status changes that the system cannot detect during
normal operation, SAM should address this issue.  Even if addressing it
consists of discussing it and then saying the SCSI architecture has no
solution (a bad idea I believe, but at least a defendable one).

Jim




                                                                                                                                       
                      Paul von Behren                                                                                                  
                      <paul.von.behren@        To:       Gerry.Houlder at seagate.com                                                     
                      sun.com>                 cc:       t10 at t10.org                                                                   
                      Sent by:                 Subject:  Re: Really getting rid of AEN                                                 
                      owner-t10 at t10.org                                                                                                
                                                                                                                                       
                                                                                                                                       
                      01/07/2003 09:25                                                                                                 
                      AM                                                                                                               
                                                                                                                                       
                                                                                                                                       




* 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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