Appendix B: Understanding RAID
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85
RAID 5EE Arrays
Note:
RAID 5EE is an upgrade feature; if the RAID 5EE feature is
locked, see
Adding Enhanced Features on page 20
purchasing a feature key.
A RAID 5EE array is similar to a RAID 5 array 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, 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 array is rebuilt following a disk drive failure.
A RAID 5EE array 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
Disk 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 Spare
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)
