Unable to umount a NFS mounted filesystem

[ricky2]

Hi All,
I'm currently facing a production issue where one NFS server mounted filesystem cannot be unmounted.
I have used all the options with umount but unable to umount.I have used the lazy unmount option ie umount -l to forcibly unmount but it has corrupted the entire data on that filesystem and I had to restore it from backup tapes.
I have already killed all the process that are found using fuser -m , lsof ..etc but when I issue umount it will say device busy.

Could anyone help me on this?

[Matti_Kurkela]

Your problem description is not quite clear to me. You're trying to unmount a filesystem, but is it a NFS filesystem you're trying to unmount at the NFS client, or is it a local filesystem at the NFS server that has been exported to clients?

If you wish to unmount a filesystem at the NFS server, you should first make all the NFS clients unmount it, then unexport the NFS directory (with exportfs -u) so that things like automounters cannot try to access the disk while you unmount it from the NFS server.

The NFS server works at the kernel level: remote NFS clients are not processes. Commands like "fuser" and "lsof" can only tell about local processes.

MK

[ricky2]

Thanks Matti,
Yes, I'm facing this issue on a local filesystem on the NFS server that has been exported to clients.

I have about 50 client machines accessing this NFS filesystem and its not possible to manually unmount it on all clients.
This filesystem is in a serviceguard cluster and whenever a failover happen it should be able to switch the filesystem to another node.