HP 381513-B21 HP Smart Array Controllers for HP Integrity Servers User Guide - Page 36

• Do not remove a second drive from an array until the first failed or missing drive has been replaced and the rebuild process is complete. (The rebuild is complete when the Online/Activity LED on the front of the drive stops blinking.) The following cases are exceptions: o In RAID 6 (ADG) configurations, any two drives in the array can be replaced simultaneously. o In RAID 1+0 configurations, any drives that are not mirrored to other removed or failed drives can be simultaneously replaced offline without data loss. Automatic data recovery (rebuild) When you replace a hard drive in an array, the controller uses the fault-tolerance information on the remaining drives in the array to reconstruct the missing data (the data that was originally on the replaced drive) and write it to the replacement drive. This process is called automatic data recovery, or rebuild. If fault tolerance is compromised, this data cannot be reconstructed and is likely to be permanently lost. If another drive in the array fails while fault tolerance is unavailable during rebuild, a fatal system error can occur, and all data on the array is then lost. In exceptional cases, however, failure of another drive need not lead to a fatal system error. These exceptions include: • Failure after activation of a spare drive • Failure of a drive that is not mirrored to any other failed drives (in a RAID 1+0 configuration) • Failure of a second drive in a RAID 6 (ADG) configuration Time required for a rebuild The time required for a rebuild varies considerably, depending on several factors: • The priority that the rebuild is given over normal I/O operations (you can change the priority setting by using ACU) • The amount of I/O activity during the rebuild operation • The rotational speed of the hard drives • The availability of drive cache • The brand, model, and age of the drives • The amount of unused capacity on the drives • For RAID 5 and RAID 6 (ADG), the number of drives in the array Allow approximately 15 minutes per gigabyte for the rebuild process to be completed. This figure is conservative; the actual time required is usually less than this. System performance is affected during the rebuild, and the system is unprotected against further drive failure until the rebuild has finished. Therefore, replace drives during periods of low activity when possible. When automatic data recovery has finished, the Online/Activity LED of the replacement drive stops blinking steadily at 1 Hz and begins to either glow steadily (if the drive is inactive) or flash irregularly (if the drive is active). Replacing, moving, or adding hard drives 36