text: Figure 6-1 Relationship between MDisks, storage pools, and volumes 
  
  Storwize V7000 organizes storage into pools to ease storage management and make it more 
  efficient. All MDisks in a pool are split into extents of the same size, and volumes are created 
  out of the available extents. The extent size is a property of the storage pool and cannot be 
  changed after the pool is created. It is possible to add MDisks to an existing pool to provide 
  additional extents or to remove extents from the pool by deleting the MDisk. 
  
  Storage pools can be further divided into subcontainers that are called*child pools*. Child 
  pools are created from existing capacity that is allocated to a parent pool. They have a similar 
  extent size setting as their parent pool and can be used for volume operation. 
  
  When you create a storage pool, you can define it to have the “Data reduction” feature 
  enabled to trigger creation of a*Data Reduction Pool (DRP)*. Data Reduction Pools increase 
  the existing infrastructure capacity utilization by leveraging new efficiency functions. Data 
  Reduction Pools automatically deallocate and reclaim capacity of thin-provisioned volumes 
  that contain deleted data. This reclaimed capacity can be reused by other volumes. Data 
  Reduction Pools also support data deduplication and compression features. 