Automatic Data Recovery (Rebuild) - HP 273914-B21 - Smart Array 6404/256 RAID Controller User Manual

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 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
Replacing, moving, or adding hard drives
In RAID ADG configurations, any two drives in the array can be
replaced simultaneously.
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.
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