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LaCie RAID Technology White Paper
RAID 3
RAID 3 uses byte-level striping with a dedicated parity disk (Disk 4 in the illustrations, right) so that one volume
mounts on the computer. A RAID 3 array can tolerate a single disk failure without data loss. If one physical disk
fails, the data from the failed disk can be rebuilt onto a replacement disk. If a second disk fails before data can
be rebuilt to a replacement drive, all data in the array will be lost.
Applications
RAID 3 provides good data safety for environ-
ments where long, sequential files are being
read, such as video files. Disk failure does not
result in a service interruption because data is
read from parity blocks. RAID 3 is useful for
people who need performance and constant
access to their data, like video editors. RAID
3 is not recommended for intensive use with
nonsequential files because random read per-
formance is hampered by the dedicated parity
disk.
A1
A4
B1
B4
C1
C4
A2
A5
B2
B5
C2
C5
A3
A6
B3
B6
C3
C6
Ap(1-3)
Ap(4-6)
Bp(1-3)
Bp(4-6)
Cp(1-3)
Cp(4-6)
RAID 3
Disk 1
Disk 2
Disk 3
Disk 4
LaCie Products with RAID 3
LaCie 4big quadra
✦
How RAID 3 Capacity Is Calculated
Each disk in a RAID 3 system should have the
same capacity.
Storage capacity in a RAID level 3 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 3 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
