What you are experiencing was standard up until Data Ontap 8.3. 8.3 introduced Advanced Drive Partitioning (ADP) which can be applied to All Flash arrays as well as "entry" level (like the 2552) arrays with any hard drive type.
In your case, spinning disks are split into two partitions - one large and one small. The "small" partitions can be used for the root aggregates. The large partitions server your data aggregates. A single fully spare disk is spare for both partition types. From a practical standpoint, it will appear as if you have twice as many disks in your system. Additionally, a whole disk is not wasted when you need such a small part of it.
You'll have to reinitialize the system from scratch to convert from standard whole disk layout to ADP layout, as the disks have to be formatted that way from the start. And you must use at least Ontap 8.3 or above - I didn't see what version of Ontap you were using, but as a new system I'd hope you were at least at 8.3.
Hope this helps.
Bob Greenwald
Senior System Engineer | cStor
NCIE SAN ONTAP, Data Protection; Flexpod Design Specialist
Kudos and accepted solutions are always appreciated.
