Subject: RE: Minutes from nfsv4 WG meeting @ 52nd IETF (Salt Lake City)

From: "Noveck, Dave" <[email-masked]>
Date: Fri, 4 Jan 2002 07:34:15 -0800

> Brian Carpenter questioned the interest in this work given
> the low turnout at the WG meeting.  Brian Pawlowski pointed
> out that the meeting did not represent those on the mailing
> list, and suggested that Rob solicit mailing list
> participants to help with replication/migration work.
> Brian Carpenter asked about support in the NFSv4 protocol
> to handle a replication/migration event, e.g. what happens
> to filehandles?  Brian Pawlowski responded that this support
> has already been designed into the protocol.

The matter is addressed but what is in V4 is probably not 
adequate for use by disparate servers participating in filesystem
migration using this protocol.  If something else is needed,
it could be added in a minor version of V4.

If the filehandles are persistent, the current model is that
they stay the same upon migration.  This was intended for
migration among homogeneous servers using a private protocol
and agreeing among themselves on the format of handles.

This isn't a very good fit for heterogenous migration.  The 
only way to use it would be for all participating servers to 
agree on an initial unique id at the front of all handles subject
to migration and then maintaining mapping table so that the new 
server can respond to old handles using the unqiue id in front
to recognize old handles.  This table would have to be persistent
and maintained as long as the old handles were considered valid.

Another option are handles that are volatile at migration.  This
has the basic problem that rebinding to expired volatile handles 
is name-based and that there are situations in whch the client 
doesn't know the current name of the file.  He might be unable
to find a file that has the name he knows or he might find one
which is not the file he had opened.  That makes migration something
that may or may not work from the applicaion point of view, rather
than something that can be relied on.

---

From: Brent Callaghan <[email-masked]>
Date: Tue, 08 Jan 2002 18:04:07 -0800

> than something that can be relied on.

Though hopefully a migration event will be more controlled than
the open slather of a fully volatile server operating continuously.
The filehandles need be "volatile" only for the duration of migration.

So, for instance, the migration servers could apply a "grace"
period that gives clients a chance to replay pathnames and
acquire new filehandles when the migration is complete.

Still no absolute guarantee of safety - but it's close.

	Brent