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LaCie RAID Technology White Paper
RAID 5+Spare
RAID 5+Spare, is a RAID 5 array in which one disk is used as spare to rebuild the system as soon as a disk
fails. At least four disks are required.
If one physical disk fails, the data remains available because it is read from the parity blocks. Data from a failed
disk is rebuilt onto the hot spare disk. When a failed disk is replaced, the replacement becomes the new hot
spare. No data is lost in the case of a single disk failure, but if a second disk fails before the system can rebuild
data to the hot spare, all data in the array will be lost.
Applications
The main advantage of RAID 5+Spare is that us-
ers can continue to access data even while the
data is rebuilt to the spare drive. RAID 5+Spare
has good data safety but disk space is limited by
the presence of the hot spare which is not used un-
til one of the other disks fails. Disk failure does not
require immediate attention because the system
rebuilds itself using the hot spare, but the failed
disk should be replaced as soon as possible.
RAID 5+Spare
Disk 1
Disk 2
Disk 3
Disk 4
Spare
A2
D2
C1
Bp
A1
B1
D1
Cp
C2
B2
Ap
Dp
LaCie Products with RAID 5+Spare
LaCie 4big quadra
✦
LaCie 5big network
✦
How RAID 5+Space Capacity Is
Calculated
Each disk in a RAID 5+Spare system should
have the same capacity.
Storage capacity in a RAID 5+Spare configu-
ration is calculated by subtracting the number
of drives by two and multiplying by the disk
capacity, or
C = (n-2)*d
where:
C = available capacity
n = number of disks
d = disk capacity
For example, in a RAID 5+Spare array with four
drives each with a capacity of 1000GB, the to-
tal capacity of the array would be 2000GB:
C = (4-2)*1000
RAID 0
RAID 1
RAID 3
RAID 3+Spare
RAID 5
RAID 5+Spare
RAID 6
RAID 0+1
RAID 10
Concatenation
JBOD
RAID Selection
