LxRoot docs

If you are using a block device on a cloud provider for backups, LxRoot uses the btrfs file system to store these. If you increase the size of the block device/volume with your cloud provider, the backup system won't automatically see the new space until you resize the file system. The command to run to do this is:-

                            btrfs filesystem resize max /mountpoint

Where /mount is your backup mount point, e.g. /backups