HP A7143A RAID160 SA Controller Support Guide

Hard Drive Installation and Replacement
Drive Failure During Rebuild
Appendix C150
Drive Failure During Rebuild
If another drive in the array fails while fault tolerance is unavailable
during rebuild, a fatal system error may occur. If this happens, all data
on the array is 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 ADG configuration
Minimizing Fatal System Errors During Rebuild
When a hard drive is replaced, the controller gathers fault-tolerance data
from the remaining drives in the array. This data is then used to rebuild
the missing data (originally on the failed drive) onto the replacement
drive. If more than one drive is removed at a time, the fault-tolerance
data is incomplete. The missing data cannot then be reconstructed and is
likely to be permanently lost.
To minimize the likelihood of fatal system errors, take these precautions
when removing failed drives:
• Do not remove a degraded drive if any other member of the array is
offline (the Online LED is off). In this condition, no other drive in the
array can be removed without data loss.
• There are some 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, as long as no
two failed drives belong to the same mirrored pair.
• When RAID ADG is used, two drives can fail simultaneously
(and be replaced simultaneously) without data loss.
• If an online spare has an unlit Online LED (it is offline), the
degraded drive can still be replaced.