Summary Of Raid Methods; Choosing A Raid Level - HP StorageWorks 1510i - Modular Smart Array User Manual

Table 7 Summary of RAID methods
Alternative name
Usable drive
space*
Usable drive space
formula
Minimum number
of physical drives
Tolerates physical
drive failure?
Tolerates
simultaneous failure
of more than one
physical drive?
Read performance
Write performance
Relative cost
*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.

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
Fault tolerance
Cost effectiveness
I/O performance
90 Storage overview
RAID 0 RAID 1+0
Striping Mirroring
100% 50%
n
n/2
1 2
Yes
No
Only if no two
No failed drives are in
a mirrored pair
High High
High Medium
Low
High
Also important
Cost effectiveness
I/O performance
Fault tolerance
I/O performance
Cost effectiveness
Fault tolerance
RAID 5 RAID 6
Distributed Data Advanced Data
Guarding (DDG) Guarding (ADG)
67% to 93% 50% to 96%
(n-1)/n (n-2)/n
3 4
Yes Yes
No Yes
High High
Low Low
Medium Medium
Suggested RAID level
RAID 6
RAID 1+0
RAID 6*
RAID 5 (RAID 0 if fault tolerance
is not required)
RAID 5 (RAID 0 if fault tolerance
is not required)
RAID 1+0