HP StorageWorks Modular Smart Array 1000 HP StorageWorks 1000/1500 Modular Sma - Page 50

Comparison of RAID methods, Choosing a RAID level, RAID 0, Most important characteristic

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Comparison of RAID methods Table 7 summarizes important features of the different RAID levels. Table 7 Summary of RAID methods RAID 0 RAID 1+0 RAID 5 Alternative name Striping Mirroring Distributed Data Guarding (DDG) Usable drive space* 100% 50% 67% to 93% Usable drive space n formula n/2 (n-1)/n Minimum number of 1 2 3 physical drives Tolerates physical drive No Yes Yes failure? Tolerates simultaneous No failure of more than one physical drive? Only if no two failed No drives are in a mirrored pair Read performance High High High Write performance High Medium Low Relative cost Low High 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. Choosing a RAID level RAID 6 Advanced Data Guarding (ADG) 50% to 96% (n-2)/n 4 Yes Yes High Low Medium 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 Also important Cost effectiveness I/O performance Fault tolerance I/O performance Cost effectiveness Fault tolerance 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 50 Storage overview

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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
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