IBM ServeRAID-4 Ultra160 Series, User Reference

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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.
2
1
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.
5
7
1
*
*
2
6
8
4
*
3
9
Chapter 3. Understanding RAID technology
21