HP Surestore Disk Array FC60 HP SureStore E Disk Array 12H User's and Service - Page 90

Concepts and Management Disk Array Features Auto Rebuild Auto Rebuild works in conjunction with Active Hot Spare to provide maximum protection against disk failure. Auto Rebuild allows the disk array to automatically begin rebuilding a failed disk drive, thus restoring data redundancy as quickly as possible. A rebuild priority setting allows you to balance array performance with rebuild speed. If a disk fails with Auto Rebuild enabled, the disk array immediately begins rebuilding the contents of the failed disk on the Active Hot Spare (or other available unallocated capacity). The disk array uses redundant information stored on the remaining disks to reconstruct the data that was on the failed disk. Until the rebuild is complete, the array is vulnerable to another disk failure and performance will be impacted. If you want more control over the rebuild process, you can disable Auto Rebuild and start a rebuild manually. This allows you to control when the rebuild is performed, but it can leave your data vulnerable to a second disk failure until the rebuild is complete. To perform a rebuild (automatic or manual), the disk array must have adequate available capacity. The best way to make this capacity available is by enabling the Active Hot Spare. This ensures that the disk array always has enough capacity to rebuild even the largest disk in the array. Rebuild Priority During a rebuild, the disk array is trying to do two things at once: perform the rebuild and service I/O requests from the host. A rebuild priority allows you to define which of these operations is more important. High rebuild priority allows the disk array to complete the rebuild as quickly as possible, but system performance may suffer because host I/Os are delayed. Low rebuild priority instructs the array to give precedence to server I/Os, thus maintaining system performance, but delaying the completion of the rebuild. Interrupted Rebuild Removing a disk from the array with Auto Rebuild enabled will cause the array controller to immediately begin a rebuild (assuming there is an Active Hot Spare or enough unallocated capacity available). If the disk is reinstalled before the rebuild is complete, the array controller will recognize the missing disk and stop the rebuild. It is not necessary for the rebuild to continue because any data on the disk that has not changed in its absence is still valid. However, data that gets written while the disk is missing must be rebuilt, so the rebuild operation might not stop. The rebuild must continue if there were any write I/Os while the disk was missing from the array. 90 Concepts