HP 166207-B21 Advanced Data Guarding User Guide - Page 10

Table 1-1, Summary of RAID Features

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1-2 Advanced Data Guarding for the Smart Array 5300 Controller Reference Guide The main advantages of RAID ADG are: I High read performance I High data availability - any two drives can fail without loss of critical data The only significant disadvantage is a relatively low write performance (lower than RAID 5), due to the need for two sets of parity data. The following table summarizes the most important features of the different varieties of RAID available. The decision chart in Figure 1-2 may help you determine which RAID option is best for your situation. Table 1-1 Summary of RAID Features RAID 0 RAID 1 / RAID 0+1 RAID 5 RAID ADG Alternative name Striping (no Mirroring fault tolerance) Distributed Data Guarding Advanced Data Guarding Usable drive space* 100% 50% 67% to 93% 50% to 96% Usable drive space n n/2 formula (n-1)/n (n-2)/n Minimum number 1 2 of hard drives 3 4 Tolerant of single No Yes hard drive failure? Yes Yes Tolerant of multiple No In RAID 0+1, only No Yes simultaneous hard when the failed drive failure? drives are not mirrored to each other Read performance High High High High Write performance High Medium Low Low Relative cost Low High Medium Medium *Note: The value for usable drive space is calculated assuming a maximum of 14 hard drives of the same capacity (or a maximum of 56 for RAID ADG) with no online spares. Compaq recommends that these maximum figures (excluding any allowable online spares) are not exceeded when configuring a drive array, due to the increased likelihood of logical drive failure with more hard drives.

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1-2
Advanced Data Guarding for the Smart Array 5300 Controller Reference Guide
The main advantages of RAID ADG are:
■
High read performance
■
High data availability – any two drives can fail without loss of critical
data
The only significant disadvantage is a relatively low write performance (lower
than RAID 5), due to the need for two sets of parity data.
The following table summarizes the most important features of the different
varieties of RAID available. The decision chart in Figure 1-2 may help you
determine which RAID option is best for your situation.
Table 1-1
Summary of RAID Features
RAID 0
RAID 1 / RAID 0+1
RAID 5
RAID ADG
Alternative name
Striping (no
fault tolerance)
Mirroring
Distributed
Data Guarding
Advanced Data
Guarding
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 hard drives
1
2
3
4
Tolerant of single
hard drive failure?
No
Yes
Yes
Yes
Tolerant of multiple
simultaneous hard
drive failure?
No
In RAID 0+1, only
when the failed
drives are not
mirrored to each
other
No
Yes
Read performance
High
High
High
High
Write performance
High
Medium
Low
Low
Relative cost
Low
High
Medium
Medium
*Note:
The value for usable drive space is calculated assuming a maximum of 14 hard drives of the same
capacity (or a maximum of 56 for RAID ADG) with no online spares. Compaq recommends that these
maximum figures (excluding any allowable online spares) are not exceeded when configuring a drive array,
due to the increased likelihood of logical drive failure with more hard drives.