IBM ServeRAID-4 Ultra160 Series User Reference page 39

Like RAID level-5, this RAID level stripes data and parity across all of the drives in
the array. When an array is assigned RAID level-5E, the capacity of the logical
drive is reduced by the capacity of two physical drives in the array (that is, one for
parity and one for the spare).
RAID level-5E offers both data protection and increased throughput, in addition to
the built-in spare drive.
Note: For RAID level-5E, you can have only one logical drive in an array. When
using RAID level-5E, you can have a maximum of seven logical drives on
the controller.
RAID level-5E requires a minimum of four drives and, depending upon the level of
firmware and the stripe-unit size, supports a maximum of 8 or 16 drives.
The following illustration is an example of a RAID level-5E logical drive.
Start with four physical drives.
Create an array using all four physical
drives.
Then, create a logical drive (labeled
as 1) within the array.
Notice that the distributed spare drive
is the free space (labeled as 2) shown
below the logical drive.
The data is striped across the drives,
creating blocks in the logical drive.
The storage of the data parity
(denoted by ) is striped, and it shifts
.
from drive to drive as it does in RAID
level-5.
Notice that the spare drive is not
striped.
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Chapter 3. Understanding RAID technology
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