Messages in this thread | | | Subject | Re: [PATCH 16/20] ceph: nfs re-export support | From | Trond Myklebust <> | Date | Thu, 16 Jul 2009 17:21:51 -0400 |
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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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