The number of drives is the only value that can be adjusted when creating the array.  Depending on the number and the type of drives selected for the new array, the RAID level  automatically adjusts. Also, the system automatically assigns spare disks. Note:  It is not possible to change RAID level or drive count of the existing array. If you must  change these properties, an array MDisk must be deleted and re-created with the required  settings. In the example that is shown in Figure 6-56, it is suggested to assign 9 drives out of the given  10 to RAID6 array. The remaining drive is assigned as a hot-spare. If you select two drives only, the system automatically creates a RAID 10 array, with no spare  drive. For more control of the array creation steps, you can select the  Internal Custom option. By default, if enough candidate drives are available, the system recommends traditional  arrays for most new configurations of MDisks. However, switch to DRAID when possible, by  using the  Internal Custom  option.  If the system has multiple drives classes (such as Flash and Enterprise disks), the default  option is to create multiple arrays of different tiers and assign them to the pool to take  advantage of the Easy Tier functionality. However, this configuration can be adjusted by  setting the number of drives of different classes to zero. For more information about Easy  Tier, see Chapter 10, “Advanced featur es for storage efficiency” on page 427. If you are adding storage to a pool with storage that is assigned, the existing storage is  considered, with some properties being inherited from existing arrays for a specific drive  class. The system aims to achieve an optimal balanced configuration, so it is not possible to  add significantly different MDisks to one pool with the GUI dialog. 254  Implementing the IBM System Storage SAN Volume Controller with IBM Spectrum Virtualize V8.2.1 Figure 6-56 Assign Storage to Pool dialog