Proxmox Backup to Empty Partition: Mount It, Add Directory Storage, Run vzdump

Proxmox backup to empty partition is easy once you mount the thing and tell Proxmox it’s directory storage. The forum answers skip the middle part, so here’s the whole path from bare partition to verified vzdump.

Mount the partition

First, find your partition. lsblk -f shows everything with filesystems. If the partition is truly empty, it won’t have one. Format it if needed:

mkfs.ext4 /dev/sdX1

Then mount it somewhere sensible. I use /mnt/backup.

mkdir -p /mnt/backup
mount /dev/sdX1 /mnt/backup

Add it to /etc/fstab so it survives a reboot. Use the UUID from blkid, not the device name. Device names can shuffle.

Add directory storage in Proxmox

Now tell Proxmox about it. Datacenter → Storage → Add → Directory. Set ID to something like backup, directory to /mnt/backup, and content type to VZDump backup file.

Or just edit /etc/pve/storage.cfg directly:

dir: backup
        path /mnt/backup
        content backup
        prune-backups keep-last=3

That prune-backups line is optional but keeps the partition from filling up with old backups. Proxmox will prune after each backup job.

Run a test backup

Pick a small VM or container and run a manual backup. In the GUI, select the VM, go to Backup now, choose backup as storage, and start it. Or from the shell:

vzdump 100 --storage backup --mode snapshot

Check the output. It should end with something like successfully backed up. Then look in /mnt/backup/dump — you should see a .vma.zst or .tar.zst file.

If it fails

Most failures are permissions. The backup user needs write access to the mount point. chown backup:backup /mnt/backup usually fixes it. If you’re using ZFS, make sure the dataset isn’t read-only. And if the partition is on a USB drive, don’t. USB drives are fine for sneaker-net backups, not for scheduled jobs.

That’s the whole thing. Mount it, add it, test it. The partition was never the hard part — it’s the two steps in between that everyone assumes you know.

Related: Proxmox Recovery Mode Doesn’t Exist: Roll Back with ZFS Snapshots, Config Backups, or GRUB