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 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)? 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. Thanks, Niels [1] http://review.gluster.org/4430
