Thank you for contacting NetApp communities. starting from Cluster mode NetApp has a special feature called Advance disk partitioning (ADP) where all your disks are shared. To explain you more what ontap does is instead of using whole dedicated disk for root volume ontap picks certain amount of size from each disk (In your case is 53.88GB) and deploy all ontap binaries during initial setup. To verify this information check commands below to confirm if your disks are shared.
storage aggregate show -fields uses-shared-disks
storage disk show -container-type shared
If you still want to corss verify log on to your Oncommand System Manager and go to aggregate and look through the disks in the bottom pane, there you can see same disk shared across aggregates (Check with Disk ID or Name) also can see description as shared.
This is by design on entry level NetApp controllers as to utlise maximum of disks.