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LaCie RAID Technology White Paper
RAID 5
RAID 5 combines the striping of RAID 0 with data redundancy in an array with a minimum of three disks.
The difference between RAID 3 and RAID 5 is that a RAID 3 configuration will offer better performance at the
expense of slightly less overall capacity. Data is striped across all disks and a parity block (P) for each data
block is written on the same stripe. If one physical disk fails, the data from the failed disk can be rebuilt onto a
replacement disk. No data is lost in the case of a single disk failure, but if a second disk fails before data can
be rebuilt to a replacement drive, all data in the array will be lost.
RAID 5
Disk 1
Disk 2
Disk 3
Disk 4
Ap
B3
C3
D3
A3
C2
D2
Bp
A2
B2
D1
Cp
A1
B1
C1
Dp
Applications
RAID 5 combines data safety with efficient use
of disk space. Disk failure does not result in a
service interruption because data is read from
parity blocks. RAID 5 is useful for archiving
and for people who need performance and
constant access to their data, like video edi-
tors.
LaCie Products with RAID 5
LaCie 4big quadra
✦
LaCie 5big network
✦
How RAID 5 Capacity Is Calculated
Each disk in a RAID 5system should have the
same capacity.
Storage capacity in a RAID level 5 configura-
tion is calculated by subtracting the number
of drives by one and multiplying by the disk
capacity, or
C = (n-1)*d
where:
C = available capacity
n = number of disks
d = disk capacity
For example, in a RAID 5 array with four drives
each with a capacity of 1000GB, the total ca-
pacity of the array would be 3000GB:
C = (4-1)*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
