No space left on device -- but there is space

I'm running an Ubuntu 12.04.1 server in a VMware virtualized environment that has a strange issue. Twice now, at seemingly random times, the machine has suddenly been unable to write to the root partition despite plenty of space seemingly available. I'm at a loss trying to figure out what's wrong.

"df -h" shows all mounted volumes with 40% or more free space. Both times this has happened, rebooting resolved it for a few minutes, and then it was back to saying "no space left on device." Restoring it from a snapshot seems to fix it for longer, but since this has now happened again, I'm not sure what to do with it.

If it helps, the machine is a network print server running CUPS 1.5.3 and Samba 3.6.3.

Solution 1:

Try with the df -i which will show you how much free inodes you have.

Basically sometimes you can run out of disk space to store metadata (data about data). That usually happens if you have a lot of small files.