4.4 local (backup) cant backup due to low storage

When you would like to use PVE as backupserver, you must destroy the default storage and add your preferred filesystemtype. Bestway for backupstorge use ZFS directly from the installer. But becareful, ZFS need more memory and no hardwareraid. 16GB+
 
You must delete the storage and create new partition. Not on web, on cmd. Delte LVM-Thin and parttions. Then create new with cfdisk, or gparted.
 
That's not really recommended. It's better do it the real way... most probably you will running in some errors with this weird config.