5.3. RAID. LaCie 5big Network

LaCie 5big Network

User Manual

RAID and Disks

page 52

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

Fig. 85

) 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

Fig. 85

A1

B1

C1

D1

Ep

Disk 1

E1

Disk 2

E2

Disk 3

A4

E3

Disk 4

Ap

B4

C4

D4

E4

Disk 5