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Appendix D: Understanding RAID ● 169
RAID 5EE Logical Drives
Note: RAID 5EE is an upgrade feature; if the RAID 5EE feature is
locked, see Adding Enhanced Features on page 21 for information on
purchasing a feature key.
A RAID 5EE logical drive is similar to a RAID 5 logical drive except that
it includes a distributed spare drive (see below) and must be built from a
minimum of four disk drives. The maximum number of disk drives is
sixteen.
Unlike a hot spare (see page 90), a distributed spare is striped evenly
across the disk drives with the stored data and parity data, and can’t be
shared with other logical disk drives. A distributed spare improves the
speed at which the logical drive is rebuilt following a disk drive failure.
A RAID 5EE logical drive protects your data and increases read and
write speeds. However, capacity is reduced by two disk drives’ worth of
space, which is for parity data and spare data.
In the example below, S represents the distributed spare, P represents
the distributed parity data.
Disk Drive 1
Disk Drive 2
Disk Drive 3
Disk Drive 4
250 GB
250 GB
400 GB
400 GB
D
isk Drives in Logical Drive
Disk Drive 1
Disk Drive 2
Disk Drive 3
Disk Drive 4
RAID 5EE Logical Drive = 500 GB plus Parity and Spa
re
1
2
S
P
Not Used
Not Used
S
P
3
4 500
S
449
P...
...
...
...
Unused Space: 150 GB
Unused Space: 150 GB
Drive Segment Size (Smallest Disk Drive)