192 Implementing the IBM Storwize V7000 with IBM Spectrum Virtualize V8.2.1
6.1  Working with storage pools
A managed disk (MDisk) is a logical unit (LU) of physical storage. MDisks are either RAID 
arrays that are constructed of internal storage disks or flash disk modules, or LUs that are 
exported from external storage systems. Storage pools act as a container for MDisks by 
dividing the MDisks into extents. Storage pools provision the available capacity from the 
extents to volumes.
Figure 6-1 provides an overview of how storage pools, MDisks, and volumes are related. 
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. 
For more information on DRP planning and implementation, see Introduction and 
Implementation of Data Reduction Pools and Deduplication, SG24-8430.
Throttles can be defined for storage pools to control I/O operations. If a throttle limit is 
defined, the system either processes the I/O for that object, or delays the processing of the 
I/O. That way resources become free for more critical I/O operations.