[Charset ISO-8859-1 unsupported, filtering to ASCII...] >T. Horsnell wrote: >> FC6, NFS V3 >> ----------- >> >> I'm trying to get to the state where >> >> 1. I can have a bunch of NFS clients which have mounted >> filesystems exported by a fileserver, >> >> 2. The fileserver is stopped, the (SCSI) disks containing >> the filesystems are moved to different positions on the SCSI bus, >> and the fileserver is rebooted. >> >> 3. The clients can still continue to access the correct filesystems, >> without having to umount/re-mount anything, even though their position >> on the server's SCSI bus has changed. >> >> The clients are members of a compute farm. They mount the NFS >> filesystems with the 'hard' option so that their NFS requests >> stall if the server is off for any reason, and so far this works >> well. However, if the server disks are moved, there are problems. >> >> >> I started off mounting the server filesystems by label, with lines >> in /etc/fstab like: >> >> LABEL=/filesys1 /filesystem1 ext3 defaults 0 2 >> >> This gave me pseudo-persistence in that wherever the disks were on >> the SCSI bus, they were always mounted on the correct mountpoint. >> With this setup, the underlying device (/dev/sda /dev/sdb etc) >> as shown by 'mount -t ext3' changed when the disk position changed. >> I then discovered that if I swapped two disks over on the server >> while those filesystems were still NFS-mounted by a client, the >> client didnt notice the swap, but continued to access the disks >> in the unswapped position, and hence access the wrong filesystem. >> There were no NFS complaints, just complaints from users. >> >> >> I'm now using a bunch of udev rules to give me device-name persistence >> instead of relying on the partition label, and I have lines in fstab like: >> >> /dev/dsk0_1 /filesystem1 ext3 defaults 0 2 >> >> Now, wherever I shift a disk to on the server SCSI bus, the underlying >> device-name stays constant, but the client objects with a 'stale NFS filehandle' >> error when the disk-position is changed, and I have to umount and remount at >> the client. Its a slight improvement in that user-processes on the client >> cant inadvertently use the wrong filesystem, but I would much prefer it to >> be transparent. Is this possible with NFS >> >> Cheers, >> Terry >> > >Yeap. > >A client knows a filesystem by server ip address, and by fsid (see >man exports), the default generated fsid is based on the underlying >device id, so if the device id changes (moved on scsi bus) >then the fsid changes, and from the clients point of view the >filesystem is no longer there. And you can get odd failures, >if someones "new" fsid matches someone elses "old" fsid you >will get interesting bad results, ie /home will say it is /home >on a client by the directories will look like /opt. If you have >large fsids it is harder to get, but I have seen it happen. > >You can in the exports file set the fsid to something, and note >that you can get into this same issue using LVM, and just adjusting >the order of turning on the VG's (first gets id 1, second 2, changing >order changes this). The fsids need to be unique across a >given server. > Aha! Many thanks for this pointer. I never noticed that option in the exports man page. I'll do some experiments straight away. Cheers, Terry. > Roger > >-- >fedora-list mailing list >fedora-list@xxxxxxxxxx >To unsubscribe: https://www.redhat.com/mailman/listinfo/fedora-list >
