In Storage Spaces a pool is a logical grouping of physical disks. There are two types of pools.
The Primordial pool represents all of the disks that Storage Spaces is able use but are not already members of a concrete pool. Physical Disks in the Primordial pool have a property named CanPool equal to “True” when they meet the requirements to create a concrete pool.
A Concrete pool is a specific collection of Physical Disks that was formed by the user to allow creating Storage Spaces (aka Virtual Disks).