HP StorageWorks 1000 Modular Smart Array - Manual (Page 50)

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
1 2 3 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 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