HP Surestore Disk Array FC60 HP SureStore E Disk Array 12H User's and Service - Page 95

Concepts and Management Disk Array Hardware Disk Cache The array controller implements caching during both reads and writes. Separate read and write caches are maintained in DRAM. The amount of cache DRAM and NVRAM can be expanded to improve performance. Controller Batteries CAUTION! Controller batteries are a vital and integral part of maintaining the memory maps during a power loss, or any time your disk array has not successfully completed a Shutdown before power off. If power is lost, and you are not using an Uninterruptable Power Supply (UPS), the batteries in the controller store the current memory maps of your data in NVRAM. Each controller module contains dual backup batteries, which provide power to the controller NVRAM when ac power to the disk array enclosure is off. Many factors affect battery life, including not only time of battery use, but also time of battery storage. Controller batteries should be replaced every three years, or sooner if the display module indicates a constant "Battery Discharged" message. Typically, a Shutdown is performed when the disk array is turned off, which copies the contents of the NVRAM to each of the physical disks in the array. If power to the array is lost before a proper Shutdown can be performed, the contents of the NVRAM must be maintained by the battery backup system until power is restored. When fully charged, the batteries are capable of sustaining the contents of the NVRAM for a minimum of one week. Disk Modules The disk modules (also referred to as "disks") provide the storage medium for the disk array. A minimum of four disk modules is required to operate the disk array. Different capacity disk modules can be installed in the same array. A new disk can be added at any time-even while the disk array is operating. The array controller will recognize that a new disk has been added, and will include the disk in the array configuration automatically if the Auto Include feature is enabled. To make the additional capacity available to the host, a new logical drive must be created, and the resulting drive must be configured into the operating system. 95 Concepts