Item

RAID 0

RAID 1+0

RAID 5

RAID 6

RAID 1(0)

 

 

 

 

(ADG)(ADM)

 

 

 

 

 

 

Alternative name

Striping (no

Mirroring

Distributed

Advanced

Advanced

 

fault

 

Data

Data

Data

 

tolerance)

 

Guarding

Guarding

Mirroring

 

 

 

 

 

 

Formula for number of drives usable

n

n/2

n-1

n-2

n/3

for data (n = total number of drives in

 

 

 

 

 

array)

 

 

 

 

 

Percentage of drive space usable*

100%

50%

67% to 93%

50% to 96%

33%

Minimum number of physical drives

1

2

3

4

3

Tolerates failure of one physical drive

No

Yes

Yes

Yes

Yes

Tolerates simultaneous failure of

No

Only if no

No

Yes

Only if no

more than one physical drive

 

two failed

 

 

three drives

 

 

drives are in

 

 

are in the

 

 

the same

 

 

same mirror

 

 

mirrored

 

 

group**

 

 

pair

 

 

 

Read performance

High

High

High

High

High

Write performance

High

Medium

Low

Low

Medium

Relative cost

Low

High

Medium

Medium

Very high

*Values for the percentage of drive space usable are calculated with these assumptions: (1) all physical drives in the array have the same capacity; (2) online spares are not used; (3) no more than 14 physical drives are used per array for RAID 5; and (4) no more than 56 drives are used with RAID 6 (ADG).

**Mirror groups include the physical drives in each mirror.

Selecting a RAID method

Not all controllers support all RAID levels. To determine the RAID capabilities of your controller, see the model-specific information for your controller on the HP website (http://www.hp.com/products/smartarray).

Most important criterionAlso importantSuggested RAID level

 

 

 

Fault tolerance

Cost effectiveness

RAID 6

 

I/O performance

RAID 10 (ADM), RAID 1+0, RAID 50, RAID 60

Cost effectiveness

Fault tolerance

RAID 6

 

I/O performance

RAID 5 (RAID 0 if fault tolerance is not required)

I/O performance

Cost effectiveness

RAID 5 (RAID 0 if fault tolerance is not required)

 

Fault tolerance

RAID 10 (ADM), RAID 1+0, RAID 50, RAID 60

Alternative fault-tolerance methods

Your operating system may also support software-based RAID or controller duplexing.

•Software-based RAID resembles hardware-based RAID, except that the operating system works with logical drives as if they were physical drives. To protect against data loss caused by physical drive failure, each logical drive must be in a different array from the others.

•Controller duplexing uses two identical controllers with independent, identical sets of drives containing identical data. In the unlikely event of a controller failure, the remaining controller and drives will service all requests.

Troubleshooting 127