[OpenAFS] Re: Volume rename with active volumes

Andrew Deason adeason@sinenomine.net
Fri, 2 Sep 2011 16:20:40 -0500

On Fri, 2 Sep 2011 17:04:10 -0400 (EDT)
Richard Brittain <Richard.Brittain@dartmouth.edu> wrote:

> As expected, most clients get an error if the vos rename has happened,
> but not the rmmount/mkmount/release (since the mount points are
> replicated).  However, a client with an open file on the volume seemed
> to be fine and continued to work after rename, and even reported the
> correct voluume name to 'fs lq'.

Clients cache vldb information (which includes name <-> id mappings, as
well as location information) for 2 hours. So if you're reading or
writing to a volume when you do the rename, the client will not notice,
since it knows it is writing to volid 1234, and doesn't care what the
name is. If you have not accessed the volume recently (or you've issued
'fs checkv', or some error causes a re-lookup), it'll try to look up the
old name and fail.

Userspace tools look up volume names / ids / etc every time they are
run, though, so 'fs lq' will interpret the volume id according to the
most recent information.

So it's not really "safe" since a client's cache could become stale
without you knowing, and it would cause accesses to that volume to
suddenly fail. That failure is a bit unlikely if you do the switch
relatively quickly, but it is certainly possible. A more safe way to do
this would be to allow you to add a volume name alias in the vldb or
something, so you could add the new name, update mountpoints, and remove
the old name. We don't provide a way to do that.

Andrew Deason