IBM ServeRAID User Reference page 45

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.
If a physical drive fails in the array,
the data from the failed drive is
reconstructed. The array undergoes
compression, and the distributed
spare drive becomes part of the array.
The logical drive remains RAID
level-5E.
When you replace the failed drive, the
data for the logical drive
decompresses and returns to the
original striping scheme.
If you use a RAID level-5E logical drive in a failover or cluster configuration, the
RAID level-5E logical drive will not failover while undergoing compression or
decompression.
RAID level-5E offers the following advantages and disadvantages.
Advantages
v 100% data protection
v Offers more physical drive storage
capacity than RAID level-1 or level-1E
v Higher performance than RAID level-5
Note: The ServeRAID Manager program Configuration wizard does not default to
RAID level-5E. If you have four physical drives, Express configuration
defaults to RAID level-5 with a hot-spare drive.
1
2
1
*
4
*
8
7
1
*
3
*
6
5
7
*
9
*
Disadvantages
v Lower performance than RAID level-1 and
level-1E
v Supports only one logical drive per array
v Cannot share a hot-spare drive with other
arrays
Chapter 3. Understanding RAID technology
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9
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2
4
*
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