According to my plan, I should have two disks, but I see just one

By default, we unite two disks into a RAID-1 unit.

We do it to protect your data. RAID-1 implies data mirroring. Both disks contain the same data.

If one of the disks is out of order, you will not lose your data. The system will keep running until the defective disk is replaced.

Note that it has nothing to do with data backup. If you delete a file, it will be removed from both disks.

RAID-1 does not guarantee the safety of your data. We recommend backing up your data.