– If performance is of concern, use a storage pool with MDisks that share the same  characteristics. Otherwise, the mirrored pair can be on external virtualized storage  with lesser-performing MDisks. GLYPH<SM590000> Data Reduction Pool (DRP) volumes  – When configuring DRP-based volumes, ther e are special considerations required and  procedures to be followed. See Chapter 3, “Data reduction and tools” on page 23. GLYPH<SM590000> Tier 0 flash: Specifies a  tier0_flash  IBM Flash Core Modules or an external MDisk for the  newly discovered or external volume. GLYPH<SM590000> Enterprise tier: Enterprise tier exists when the pool contains enterprise-class MDisks,  which are disk drives that are optimized for performance.  GLYPH<SM590000> Tier 1 flash: Specifies a  tier1_flash  (or flash SSD drive) for the newly discovered or  external volume. GLYPH<SM590000> Nearline tier: Nearline tier exists when the pool contains nearline-class MDisks, which are  disk drives that are optimized for capacity. Note:  In the IBM FlashSystem 9100 these Enterprise or Nearline drives would be in  external arrays. All managed arrays on the IBM FlashSystem 9100 system contain  either NVMe class drives in the IBM FlashSystem 9100 control enclosures, or SSD  class drives in the SAS expansion enclosures.  All MDisks belong to one of the tiers, which includes MDisks that are not yet part of a pool. If the IBM FlashSystem 9100 control enclosure is used in an Easy Tier pool and is enabled on  the pool, the node canisters will send encrypted, incompressible data to the NVMe drives.  IBM Spectrum Virtualize software detects if an MDisk is encrypted by the FlashSystem 9100.  Therefore, if an IBM FlashSystem 9100 control enclosure will be part of an encrypted  easy-tier pool, encryption must be enabled on the IBM FlashSystem 9100  before  it is enabled  in the Easy Tier pool.  IBM Spectrum Virtualize does not attempt to encrypt data in an array that is already  encrypted. This enables the hardware compression of the IBM FlashSystem 9100 to be  effective if using the FCM type NVMe drives. However, there are cases in which using IBM  FlashSystem 9100 software compression is preferred, such as if there is highly compressible  data, (for example 3:1 or higher). In these cases, both encryption and compression can be  done by the IBM FlashSystem 9100 node canisters.  Storage pools have an Easy Tier setting that controls how Easy Tier operates. The setting  can be viewed through the management GUI but can only be changed by the CLI. For more information about Easy Tier, see the IBM Redbooks publication  Implementing the  IBM System Storage SAN Volume Controller with IBM Spectrum Virtualize V8.1 , SG24-7933.  In addition, see the Easy Tier function section in the FlashSystem 9100 IBM Knowledge  Center. Chapter 4. Planning  107 IBM Easy Tier is a function that automatically and non-disruptively moves frequently  accessed data from various types of MDisks to flash drive MDisks, thus placing such data in a  faster tier of storage. Easy Tier supports four tiers of storage.  The IBM FlashSystem 9100 supports the following tiers: 4.6.3 Easy Tier 