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SubjectRe: [PATCH 16/20] ceph: nfs re-export support
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On Thu, 2009-07-16 at 12:50 -0700, Sage Weil wrote:
> On Thu, 16 Jul 2009, J. Bruce Fields wrote:
> > On Wed, Jul 15, 2009 at 02:24:46PM -0700, Sage Weil wrote:
> > > Basic NFS re-export support is included. This mostly works. However,
> > > Ceph's MDS design precludes the ability to generate a (small)
> > > filehandle that will be valid forever, so this is of limited utility.
> >
> > Is there any hope of fixing that?
>
> Yes, but it requires some additional ondisk metadata the MDS isn't
> maintaining yet (a parent directory backpointer on file objects).
>
> The MDS changes will mean more random IO for rename intensive workloads,
> but the backpointers would also be useful for rebuilding the directory
> tree in the event of some catastrophic metadata loss or corruption.
> (Currently they're only there for directories, not all files.)

Note that a filehandle that contains parent directory information is
still not one that is valid forever. It will change in the case of a
cross-directory rename, and so isn't a filehandle in the NFSv2/v3 sense.
Even in the NFSv4 case, it would have to be labelled as 'volatile'.

Cheers
Trond



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