Several disks for server storage file system

Hello,
I am testing urbackup : it works very well and is very easy to setup and use !
Then I try to understand up to which extend I can use it.
In admin manual, I read
"

8.1 Global Server Settings

8.1.1 Backup storage path

The backup storage path is where all backup data is saved.
To function properly all of this directories’ content must lie on the same file system (otherwise hard links cannot be created).
"

I would like to be sure understand what this means.
As an example, if I store data under : media/urbackup
I can : mount -t btrfs /dev/sdb media/urbackup…
This means only ONE disk for media/urbackup, which is very limitative.

How can I manage a dedicated server with 4*4Tb storage capability for example.
Thank you very much for your help.

E.g. https://en.wikipedia.org/wiki/Mdadm https://wiki.archlinux.org/index.php/RAID https://raidsim.urbackup.org/

RAID was unclear to me !
Thank you very much :grinning: