LaCie 4big Quadra
• D
esign
by
N
eil
P
oulton
RAID
User Manual
page 17
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
RAID 3+ Spare
Disk 1
Disk 2
Disk 3
Disk 4
A1
A3
B1
B3
C1
C3
A2
A3
B2
B4
C2
C4
Ap(1-2)
Ap(3-4)
Bp(1-2)
Bp(3-4)
Cp(1-2)
Cp(3-4)
Spare
RAID 3 and RAID 3+Spare
3.1.4.
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 with-
out 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.
In RAID 3+Spare
, one disk in the array is left empty. If a drive
in the array fails, the data from the failed disk is automatically
rebuilt to the empty or “spare” disk.
Applications
RAID 3 provides good data safety for environments where
long, sequential files are being read, such as video files.
Disk failure does not result in a service interruption be-
cause 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 performance is hampered by the dedicated parity
disk
In RAID 3+Spare
disk failure does not require immedi-
ate attention because the system rebuilds itself using the
hot spare, but the failed disk should be replaced as soon
as possible.
