User manual

2.3 RAID Levels

2.3.1 Disk Striping (RAID 0)

Striping is a performance-oriented, non-redundant data mapping technique. While Striping is discussed as a RAID Group type,

it is does not provide any fault tolerance. With modern SATA and ATA bus mastering technology, multiple I/O operations can

be performed in parallel, enhancing data throughput. Striping arrays use multiple disks to form a larger virtual disk. The figure

below illustrates a three-disk stripe set. Stripe one is written to disk one, stripe two to disk two, and so forth. RAID 0 sets can

be comprised of two, three, or four drives.

Stripe2

Stripe5

Stripe8

Stripe11

Stripe0

Stripe3

Stripe6

Stripe9

Stripe1

Stripe4

Stripe7

Stripe10

2.3.2 Disk Mirroring (RAID 1)

Disk mirroring creates an identical twin for a selected disk by having the data simultaneously written to two disks. This

redundancy provides instantaneous protection from a single disk failure. If a read failure occurs on one drive, the system reads

the data from the other drive. RAID 1 sets are comprised of two drives. A third drive can be allocated as a spare in case one

of the drives in the set fails.

k 1

k 2

k 1

k 2

2.3.3 Disk Mirroring and Striping (RAID 10)

RAID 10 combines the features of both RAID 0 and RAID 1. Performance is provided through the use of Striping (RAID 0),

while adding the fault tolerance of Mirroring (RAID 1). The implementation of RAID 10 requires four drives. The drives are

assigned as two sets of striped pairs.

The data is written to RAID Group A, which is striped (RAID 0). This allows maximum speed. The data is then mirrored to

another RAID 0 striped set, which is Set B in the figure above. This provides data redundancy (RAID 1), and thus increased

data security.

Under certain circumstances, a RAID 10 set can sustain multiple simultaneous drive failures.

2.3.4 Parity RAID (RAID 5)

Parity or RAID 5 adds fault tolerance to Disk Striping by including parity information with the data. Parity RAID dedicates the

equivalent of one disk for storing parity stripes. The data and parity information is arranged on the disk array so that parity is