Backup issues - no space left on device??

Greetings,

I received the following error on my last backups:

Backing up Webmin ACL files .. .. done

Backing up AWstats configuration file .. .. done

Creating TAR file of home directory .. .. TAR failed! cat: write error: No space left on device

gzip: stdout: Broken pipe /bin/tar: -: Cannot write: Broken pipe /bin/tar: Error is not recoverable: exiting now

But when do a 'df -h' I assume I have plenty of space:

root@box:~# df -h Filesystem Size Used Avail Use% Mounted on /dev/xvda1 4.0G 1.4G 2.7G 34% /

udev 4.9G 4.0K 4.9G 1% /dev

tmpfs 2.0G 252K 2.0G 1% /run

none 5.0M 0 5.0M 0% /run/lock

none 4.9G 0 4.9G 0% /run/shm

/dev/mapper/vg00-usr 4.0G 1.3G 2.6G 34% /usr

/dev/mapper/vg00-var 4.0G 1.7G 2.2G 43% /var

/dev/mapper/vg00-home 59G 16G 41G 28% /home

Can someone tell me where Virtualmin is storing the intermediate .tar? The website uses 1.88 GB (1.89 GB by server administrator, 0 bytes by mail / FTP users), and has no quota enabled.... I´m somewhat stuck at the moment, any help would be highly appreciated.

Cheers Johannes