For greatest control and flexibility, you can use the mkarray  command-line interface (CLI) command to configure a nondistributed array on your system. However, the suggested organization for the IBM FlashSystem 9100 is to configure a distributed array (DRAID6). You can use the mkdistributedarray  command to do this. 

Note:  DRAID6 arrays give better performance and rebuild times in the event of a FCM or NVMe drive failing, because the spare capacity allocated for the rebuild is shared across all of the drives in the system, and not reserved to one physical drive, as we have in the traditional RAID arrays. 

Additionally, MDisks are also created for each external storage-attached LUN assigned to the IBM FlashSystem 9100 as a managed or as un-managed MDisk for migrating data. A managed MDisk is an MDisk that is assigned as a member of a storage pool: 

GLYPH<SM590000> A storage pool is a collection of MDisks. An MDisk can only be contained within a single storage pool. 

GLYPH<SM590000> IBM FlashSystem 9100 can support up to 1,024 storage pools. 

GLYPH<SM590000> The number of volumes that can be allocated per system limit is 10,000. 

GLYPH<SM590000> Volumes are associated with a single storage pool, except in cases where a volume is being migrated or mirrored between storage pools. 

Information:  For the most up-to-date IBM FlashSystem 9100 configuration limits, go to the configuration for the IBM FlashSystem 9100 family. 

## Extent size 

Each MDisk is divided into chunks of equal size called extents . Extents are a unit of mapping that provides the logical connection between MDisks and volume copies. 

The extent size is a property of the storage pool and is set when the storage pool is created. All MDisks in the storage pool have the same extent size, and all volumes that are allocated from the storage pool have the same extent size. The extent size of a storage pool cannot be changed. If you want another extent size, the storage pool must be deleted and a new storage pool configured. 

The IBM FlashSystem 9100 supports extent sizes of 16 MB, 32 MB, 64 MB, 128 MB, 256 MB, 512 MB, 1024 MB, 2048 MB, 4096 MB, and 8192 MB. By default, the MDisks created for the internal storage of flash memory in the IBM FlashSystem 9100 are created with an extent size of 1024 MB. To use a value that differs from the default requires the use of CLI commands to delete and re-create with different value settings. For information about the use of the CLI commands, search for CLI commands in IBM Knowledge Center. 

