storage pool

A unit of storage made up of one or more disks. By default, MapR storage pools contain two or three disks. For high-volume reads and writes, you can create larger storage pools when initially formatting storage during cluster creation.
Remember: Storage pool refers to the combined storage capacity that is obtained by combining one or more storage devices. Storage devices can be anything from a very small disk drive to large arrays of disk drives (each containing 20-30 drives).

A storage pool is created to get a very large capacity of GBs/TBs/PBs available, from which users are provided needed amounts of storage

For example, one can combine 10 hard disk drives of 4TB each, totaling to 40TBs. Now, one can either directly use the 40TB as a single device or partition the space out to many smaller storage capacities such as 100GB, 1TB and so on from this 40TB and provide that access to different users.