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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:
◦
If 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.
◦
If 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)
If 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).
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 HPE Smart Storage Administrator)
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
Automatic data recovery (rebuild)
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