Re: [nfsv4] LAYOUTCOMMTI clarifications (was Notes from Bakeathon (re-sending))

On 2010-10-21 18:54, Trond Myklebust wrote:
> On Thu, 2010-10-21 at 16:40 +0000, Spencer Shepler wrote:
>> For the LAYOUTCOMMIT issues, at this point it seems some text
>> is needed to further discussion towards closure.  This doesn't 
>> need to be in the form of an I-D at this point given that,
>> as Dave points out, may be an errata for the RFCs.
> 
> I am planning to contribute some errata text for this. I'll notify the
> list as soon as I have a more or less final draft (hopefully in the next
> few days).

I agree that the existing text needs to be clarified, given
the level of discussions we had about it. Thanks!

Though, to me it was pretty clear that we roughly reached consensus (lower
case, not ietf ROUGH CONSENSUS ;-) that LAYOUTCOMMIT is always required for
maintaining stable storage semantics. So, for example the client should not
drop dirty data out of its cached until that data is stable at the DS
and a respective LAYOUTCOMMIT was successfully processed by the server.

It is true that for some server implementations of the files layout,
LAYOUTCOMMIT might be superfluous as they have a state coherent back-end
protocol allowing the MDS and DS to implicitly keep files' metadata in sync
but there could be files-based servers implementing loosely coupled DSs
that will still require LAYOUTCOMMIT from the client for efficient
operation.

I also mentioned Dave Noveck's unofficial proposal from long ago to
extend the WRITE operation response stable_how4 with a LAYOUT_SYNC4 value:

   enum stable_how4 {
           UNSTABLE4       = 0,
           DATA_SYNC4      = 1,
           FILE_SYNC4      = 2
+          LAYOUT_SYNC4    = 3
   };

LAYOUT_SYNC4 on the DS means that the DS data, local metadata, and layout
are on stable storage and so the client does not need to send COMMIT to the DS
nor LAYOUTCOMMIT to the MDS.

Benny

> 
> Cheers
>   Trond
> 
>> Spencer
>>
>>
>>> -----Original Message-----
>>> From: nfsv4-bounces@ietf.org [mailto:nfsv4-bounces@ietf.org] On Behalf Of
>>> sfaibish
>>> Sent: Thursday, October 21, 2010 8:56 AM
>>> To: nfsv4 list
>>> Subject: [nfsv4] Fwd: Notes from Bakeathon (re-sending)
>>>
>>>
>>>
>>> ------- Forwarded message -------
>>> From: sfaibish <sfaibish@emc.com>
>>> To: "nfsv4 list" <nfsv4@ietf.org>
>>> Cc:
>>> Subject: Notes from Bakeathon (re-sending)
>>> Date: Thu, 21 Oct 2010 11:46:17 -0400
>>>
>>>
>>>
>>> ------- Forwarded message -------
>>> From: sfaibish <sfaibish@emc.com>
>>> To: "nfsv4 list" <nfsv4@ietf.org>
>>> Cc:
>>> Subject: Notes from Bakeathon
>>> Date: Thu, 21 Oct 2010 10:11:13 -0400
>>>
>>> As I promissed I worked on the notes from the discussions at BAT.
>>> Attached please find some notes and presentations I want to post on the
>>> BAT web site. Please take a look and see if they are appropriate for
>>> posting. Also feel free to comment discuss in the list the notes and the
>>> discussions. Thank you all
>>>
>>> /Sorin
>>>
>>>
>>>
>>> --
>>> Best Regards
>>>
>>> Sorin Faibish
>>> Corporate Distinguished Engineer
>>> Unified Storage Division
>>>          EMC²
>>> where information lives
>>>
>>> Phone: 508-249-5745
>>> Cellphone: 617-510-0422
>>> Email : sfaibish@emc.com
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