Raid 5 - LaCie 5big network User Manual

LaCie 5big network
User Manual
5.3.

RAID 5

In RAID 5, data is striped across all disks (minimum of three) and
a parity block for each data block (P in the diagram at left) 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.
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 editors.
How RAID 5 Capacity Is Calculated
Each disk in a RAID 5system should have the same capacity.
Storage capacity in a RAID level 5 configuration 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 capacity of the array would be
3000GB:
C = (4-1)*1000
RAID 5
A1 A2 A2 A3 A3
B1 B2 B2 Bp B3
C1 C2 Cp Cp C2
D1 Dp D1 D2 D2
Ep E1 E2
Disk 1 Disk 2 Disk 3
RAID and Disks
page 51
A4 Ap
Bp B3 B4
C3 C3 C4
D3 D3 D4
E3 E4
Disk 4 Disk 5