On Wed, Jan 30, 2013 at 02:31:09PM -0500, bfields wrote: > On Fri, Jan 25, 2013 at 03:23:28PM +0100, Niels de Vos wrote: > > Hi all, > > > > the last few days I have been looking into making the tracking of > > NFS-clients more persistent. As it is today, the NFS-clients are kept in > > a list in memory on the NFS-server. When the NFS-server restarts, the > > list is recreated from scratch and does not contain the NFS-clients that > > still have the export mounted (Bug 904065). > > > > NFSv3 depends on the MOUNT protocol. When an NFS-client mounts an > > export, the MOUNT protocol is used to get the initial file-handle. With > > this handle, the NFS-service can be contacted. The actual services > > providing the MOUNT and NFSv3 protocol can be separate (Linux kernel > > NFSd) or implemented closely together (Gluster NFS-server). > > > > Now, when the Linux kernel NFS-server is used, the NFS-clients are saved > > my the rpc.mountd process (which handles the MOUNT protocol) in > > /var/lib/nfs/rwtab. This file is modified on mounting and unmounting. > > Implementing a persistent cache similar to this is pretty straight > > forward and is available for testing and review in [1]. > > > > There are however some use-cases that may require some different > > handling. When an NFS-server starts to mount an export, the MOUNT > > protocol is handled on a specific server. After getting the initial > > file-handle for the export, any Gluster NFS-server can be used to talk > > NFSv3 and do I/O. When the NFS-clients are kept only on the NFS-server > > that handled the initial MOUNT request, and due to fail-over (think CTDB > > and similar here) an other NFS-server is used, the persistent cache of > > 'connected' NFS-clients is inaccurate. > > > > The easiest way I can think of to remedy this issue, is to place the > > persistent NFS-client cache on a GlusterFS volume. When CTDB is used, > > the locking-file and is placed on a shared storage as well, so the same This is the statd data? That's the more important thing to get right. > > volume can be used for the NFS-client cache. Providing an option to set > > the volume/path of the NFS-client cache would be needed for this. > > I guess that this could result in a chicken-and-egg situation > > (NFS-server is started, but no volume mounted yet)? I don't think there should be any problem here: the exported filesystems need to be available before the server starts anyway. (Otherwise the only response the server could give to operations on filehandles would be ESTALE.) --b. > > > > Any ideas or recommendations are welcome. The patch in [1] is not final > > yet and I'd like some feedback before I proceed any further. > > My only comment is that this doesn't need to be perfect or even all that > good. > > The list can already get out of sync in other ways: clients can just > fail to unmount, for example. > > I don't think it's used by anything other than showmount.
