
Table 7 Summary of RAID methods
RAID 0 RAID 1+0
RAID 5 RAID 6
Alternative name
Striping Mirroring
Distributed Da
ta
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
1
23
4
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 f
orusabledrivespacearecalculatedwiththeseassumptions:
• All physi
cal drives in the array have the same capacity.
• Online sp
ares are not used.
• No more t
han14physicaldrivesareusedperarrayforRAID5.
• No more t
han 56 drives are used with RAID 6.
Choosing a RAID level
Use Table 8 to help you determine the best RAID level for your environment.
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
RAID5(RAID0iffaulttolerance
is not required)
I/O performance Cost effectiveness
RAID5(RAID0iffaulttolerance
is not required)
Fault
tolerance
RAID 1+0
90 Storage overview
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