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## 6.1 Working with storage pools 

A managed disk (MDisk) is a logical unit (LU) of physical storage. MDisks are 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. 

An overview of how storage pools, MDisks, and volumes are related is shown in Figure 6-1. 

<img src='content_image/1004681.jpg'>

IBM SAN Volume Controller 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 a pool to provide more 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 a storage pool is created, you can define it to have the Data reduction feature enabled. This feature creates a Data Reduction Pool  (DRP). DRPs increase infrastructure capacity use by using new efficiency functions. DRPs enable you to automatically de-allocate and reclaim capacity of thin-provisioned volumes that contain deleted data and enable this reclaimed capacity to be used by other volumes. DRPs also support data deduplication and compression features. 

For more information about DRP planing 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 processes the I/O for that object, or delays the processing of the I/O to free resources for more critical I/O operations. You can create an IOPS, bandwidth limit, or both. 

