HP Surestore Disk Array FC60 HP SureStore E Disk Array 12H User's and Service - Page 101

Concepts and Management Managing the Disk Array Capacity Sample Capacity Allocation The following example illustrates how the disk array uses capacity in a typical configuration. In this example there are eight disks installed in the array: four 2-Gigabyte disks and four 1-Gigabyte disks. Active Hot Spare is enabled for maximum data protection. This explanation describes how information is logically distributed. Physically, the information is spread evenly throughout all the disks. Figure 25. Capacity Allocation Starting with 12 Gigabytes of disk storage, the capacity is distributed as follows: • Gigabytes for Active Hot Spare - When using Active Hot Spare, the disk array always reserves enough capacity to rebuild the largest disk, which in this example is 2 Gigabytes. • Gigabytes for parity - This is the capacity used to support the data protection provided by RAID 5. When using disks of different sizes, the disk array divides the capacity into segments. To ensure adequate protection for all the data, parity must be maintained for each segment. In this example, 1 Gigabyte of parity is required for the upper segment, and 1 Gigabyte for the lower segment. • Gigabytes for RAID 0/1 and controller overhead - This is the capacity used by the disk array to support dynamic data migration and maintain performance. This calculation is approximate and will vary as more disks are added or removed. • Gigabytes available capacity - This is the capacity used for creating logical drives (LUNs). It represents the total amount of capacity available to the host. 101 Concepts