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50 Storage overview

Comparison of RAID methods

Table 7 summarizes important features of the different RAID levels.

Choosing a RAID level

Use Table 8 to help you determine the best RAID level for your environment.

Table 7 Summary of RAID methods

RAID 0 RAID 1+0 RAID 5 RAID 6

Alternative name Striping Mirroring Distributed Data

Guarding (DDG)

Advanced Data

Guarding (ADG)

Usable drive space* 100% 50% 67% to 93% 50% to 96%

Usable drive space

formula

n n/2 (n-1)/n (n-2)/n

Minimum number of

physical drives

1234

Tolerates physical drive

failure?

No Yes Yes Yes

Tolerates simultaneous

failure of more than

one physical drive?

No Only if no two failed

drives are in a mirrored

pair

No Yes

Read performance High High High High

Write performance High Medium Low Low

Relative cost Low High Medium Medium

*Values for usable drive space are calculated with these assumptions:

• All physical drives in the array have the same capacity.

• Online spares are not used.

• No more than 14 physical drives are used per array for RAID 5.

• No more than 56 drives are used with RAID 6.

Table 8 Choosing a RAID level

Most important characteristic Also important Suggested RAID level

Fault tolerance Cost effectiveness RAID 6

I/O performance RAID 1+0

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 1+0

1 2 ... 45 46 47 48 49 50 51 52

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