Suppose you created a datastore of 5TB in the new Proxmox Backup and wish to increase this, the process isn't quite as simple as in Proxmox VE.

If you're running Proxmox Backup as a VM, you should first increase the disk size for Proxmox Backup in Proxmox itself. This of course doesn't increase the datastore size automatically in Proxmox Backup which is what the following commands will achieve.

Start by identifying the disk path for the datastore you wish to increase:

df -h

Assuming the path is /dev/sdb1 use fdisk to start the process:

fdisk /dev/sdb

Next take note of the values in the START and END columns when issuing the following:

p

Next, delete the partition by issuing the following:

d

and then press the following to delete partition 1:

1

This will NOT delete the data, but rather allow us to remap the start and end positions of the partition table.

Now, create a new partition by issuing the following:

n

Ensure that the START position is as noted above. It should be by default. The END position should also now be the end of the disk which is the default. As such, press enter, and then enter again.

Next, write the changes made above to disk with the following:

w

And now press enter.

Finally, exit fdisk and resize the disk with the following:

resize2fs /dev/sdb1

If you don't see the changes, reboot the machine and you should be good to go.