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I've posted that on StackOverflow and I've been advised to move it here. Sorry for that.

First of all, this is the first time I'm posting a question on ServerFault, 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.

  • How are you doing the backups? What kind of VMs backed up with what software? Are the VMs running (and changing) during the backups? – Sven Aug 25 '14 at 11:21
  • What is the source? LVM volumes? Container files? Are they live and changing? If they are, this can't work and this is not an NFS fault. – Sven Aug 25 '14 at 11:25
  • The backups are done with "dd": sh -c /bin/dd if=/dev/vg_vps/nt3dxsk4tn bs=24M iflag=direct | gzip -c > /back/20140825/110.img.gz 2>&1 Those are KVM VMs. And yes, the VMs are running during the backup process. – jrance Aug 25 '14 at 11:25
  • When the backup is directly done on the local FS, everything goes fine. We do only face issues when making a backup directly on the NFS mount point. – jrance Aug 25 '14 at 11:27
  • OK, and what happens if you copy the local backup to the NFS volume? Beside that, this will not give you reliable backups, NFS or not, as the file system inside the container will be inconsistent. Quiesce the file systems inside the VMs, make an LVM snapshot and backup this. – Sven Aug 25 '14 at 11:30
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This may be an old question, but I hope answering it may still be useful to folks with the same problem...

The problem with failed data transfers indeed arises from network outages. The culprit here is the soft option used when mounting the NFS export. If there are too many failed retries, the data transfer fails with an error code. To avoid this, try using the hard option instead - that causes the backup process to retry transmitting data until it can successfully continue to do so. You may then remove the timeo and retrans options since they aren't needed any more.

I'm making use of NFS mounts myself, and I'd always use the hard option to avoid data loss.

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