“Unstable” NFS mount point

Question

First of all, this is the first time I'm posting a question on StackOverflow, so please don't kill me if I've done anything wrong.

There goes my issue:

We have few dedicated servers with a well known French provider. With one of those servers ewe have recently acquired a 5.000GB backup space which can be mounted via NFS, and that's what we've done.

The issue comes when backing up big files. Every night we back up several VM's running on that host and we know from fact that the backups are not being properly done (the file size differs a lot from one day to the other plus we've checked the content of the backup and there's stuff missing).

So, it seems like the mount point is not stable and the backups are not being properly done. Seems like there are micro network cuts and therefore the hypervisor finishes the current backup and starts with the next one.

This is how it's mounted right now:

xxx.xxx.xxx:/export/ftpbackup/xxx.ip-11-22-33.eu/ /NFS nfs auto,timeo=5,retrans=5,actimeo=10,retry=5,bg,soft,intr,nolock,rw,_netdev,mountproto=tcp 0 0

Any advise? Is there any parameter you would change?

We need to be sure that the NFS mount point is correctly working in order to have proper backups.

Thank you so much

Answer 1

By specifying "soft" as an option, you're saying that it's OK for the mount to be unreliable -- for the kernel to return an I/O error instead of running the I/O to completion when things are taking too long. Using a hard mount, without the "soft" option instructs the kernel to avoid returning I/O errors for timeouts.

This will fix your corrupted backups, but... your backup process will hang hard until I/O's complete. An alternative is to use much longer timeout values.

You're using TCP for the mount protocol, but not for NFS itself. If your server supports it, consider adding "tcp" to the options line.