HP Smart Array 6i Controller and 128MB BBWC - Manual (Page 37)

37
Probability of Logical Drive Failure
In This Section
Factors Involved in Logical Drive Failure.................................................................................... 37
Factors Involved in Logical Drive Failure
The probability that a logical drive will fail depends on the RAID level setting
and on the number and type of physical drives in the array. If the logical drive
does not have an online spare, the following results apply:
•
A RAID 0 logical drive fails if only one physical drive fails.
•
A RAID 1+0 logical drive fails if any two failed physical drives are mirrored
to each other.
−
The maximum number of physical drives that can fail without causing
failure of the logical drive is n/2, where n is the number of hard drives in
the array. In practice, a logical drive usually fails before this maximum is
reached. As the number of failed physical drives increases, it becomes
increasingly likely that the newly failed drive is mirrored to a previously
failed drive.
−
The minimum number of physical drive failures that can cause the
logical drive to fail is two. This situation occurs when the two failed
drives are mirrored to each other. As the total number of drives in the
array increases, the probability that the only two failed drives in an array
are mirrored to each other decreases.
•
A RAID 5 logical drive fails if two physical drives fail.
•
A RAID ADG logical drive fails when three physical drives fail.
HP CONFIDENTIAL
File Name: 347914-1.doc Last Saved On: 1/26/04 9:31 AM