Draft Document for Review December 5, 2019 4:33 pm 8456ch_Virtualization_Concepts.fm 4.3 Abstraction layers for drive virtualization 4.3.1 Array sites 4.3.2 Arrays Chapter 4. Virtualization concepts  101 Virtualization in the DS8900F refers to the process of preparing physical drives for storing  data that belongs to a volume that is used by a host. This process allows the host to think that  it is using a storage device that belongs to it, but it is really being implemented in the storage  system. In open systems, this process is known as creating logical unit numbers (LUNs). In  IBM Z, it refers to the creation of 3390 volumes.  The basis for virtualization begins with the  physical drives,  which are mounted in storage  enclosures and connected to the internal storage servers. DS8900F only uses the  High-Performance Flash Enclosure Gen2 (HPFE Gen2) storage enclosures. To learn more  about the drive options and their connectivity to the internal  storage servers , see 2.5, “Flash  drive enclosures” on page 50. Virtualization builds upon the physical drives in a series of layers: An  array site  is formed from a group of eight identical drives with the same capacity, speed,  and drive class. The specific drives that are assigned to an array site are automatically  chosen by the system at installation time to balance the array site capacity across both drive  enclosures in a pair, and across the connections to both storage servers. The array site also  determines the drives that are required to be reserved as spares. No predetermined storage  server affinity exists for array sites.  Array sites are the building blocks that are used to define  arrays . An  array  is created from one  array site.  When an array is created, its Redundant Array of  Independent Disks (RAID) level, array type, and array configuration are defined. This process  is also called  defining  an array. In all DS8000 series implementations, one array is always  defined as using one array site. The following RAID levels are supported in DS8900F: An RPQ is required for flash drives greater than 1 TB (RPQ is not available for drive sizes  of 4 TB and over). Each HPFE Gen2 pair can contain up to six array sites. The first set of 16 flash drives creates  two 8-flash-drive array sites. RAID 6 arrays will be created by default on each array site.  RAID 5 is optional for flash drives smaller than 1 TB, but is not advised. RAID 10 is optional  for all flash drive sizes, except for the 7.68 TB and 15.36 TB Flash Tier 2 drives. GLYPH<SM590000> RAID 6 (default) GLYPH<SM590000> RAID 10 GLYPH<SM590000> RAID 5 (possible for flash drive sizes below 1 TB) GLYPH<SM590000> Array sites GLYPH<SM590000> Arrays GLYPH<SM590000> Ranks GLYPH<SM590000> Extent pools GLYPH<SM590000> Logical volumes GLYPH<SM590000> Logical subsystems