HP 60-Modular-Smart-Array - Manual (Page 31)

Troubleshooting 31
• Open HP SIM and inspect the Error Counter window for each physical drive in the same array to
confirm that no other drives have any errors. (For details, refer to the HP SIM documentation on the
Management CD.)
• Be sure that the array has a current, valid backup.
• Use replacement drives that have a capacity at least as great as that of the smallest drive in the
array. The controller immediately fails drives that have insufficient capacity.
To minimize the likelihood of fatal system errors when removing failed drives, take the following
precautions:
• Do not remove a degraded drive if any other drive in the array is offline (the online LED is off). In this
situation, removing any other drive in the array causes data loss.
Exceptions:
• When RAID 1+0 is used, drives are mirrored in pairs. Several drives can be in a failed condition
simultaneously (and they can all be replaced simultaneously) without data loss, if no two failed
drives belong to the same mirrored pair.
• When RAID 6 with ADG is used, two drives can fail simultaneously (and be replaced
simultaneously) without data loss.
• If the offline drive is a spare, the degraded drive can be replaced.
• 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 LED on the front of the
drive stops blinking.)
Exceptions:
• 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.
• In RAID 6 with ADG configurations, any two drives in the array can be replaced simultaneously.
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
may 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 with 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