Sample Capacity Allocation - HP Surestore Disk Array 12h - And FC60 Service Manual

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.
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.
Figure 25. Capacity Allocation
Concepts and Management
Managing the Disk Array Capacity
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