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.

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 DS8880 storage arrays can be configured as RAID 6, RAID 10, or RAID 5, depending on the drive type. RAID 6 is now the default and preferred setting for the DS8880. RAID 5 can be configured for drives of less than 1 TB, but this configuration is not preferred and requires a risk acceptance, and a field request price quotation (RPQ) for Enterprise HDD drives. Drive sizes larger than 1 TB (but not Nearline drives) can be configured using RAID 5, but require an RPQ and an internal control switch to be enabled. RAID 10 continues to be an option for all drive types except Tier 2.

During logical configuration, arrays and spares are created from groups of eight drives (array sites). The required number of spares for each DA pair is four drives of the same capacity and speed. For example, the first four RAID 6 arrays that are created are 5+P+Q+S. Additional RAID 6 arrays (of the same capacity and speed) that are configured on the DA pair are 6+P+Q. The next group of 16 drives creates two 8-drive array sites. These next two arrays to be created from these array sites are 6+P+Q.

For more information on virtualization and its many layers and RAID configurations, see relevant chapters in the following IBM Redbooks publications: