HP Smart Array 6i Controller and 128MB BBWC - Manual (Page 47)

Drive Arrays and Fault-Tolerance Methods 47
HP CONFIDENTIAL
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Write performance High Medium Low Low
This method is most useful when data loss is unacceptable but cost is also an
important factor. The probability that data loss will occur when an array is
configured with RAID ADG is less than it would be if it were configured with
RAID 5.
Advantages:
•
Has a high read performance.
•
Allows high data availability—any two drives can fail without loss of critical
data.
•
More drive capacity is usable than with RAID 1+0—parity information
requires only the storage space equivalent to two physical drives.
Disadvantages:
The main disadvantage of RAID ADG is a relatively low write-performance
(lower than RAID 5), because of the need for two sets of parity data.
Comparing the Hardware-Based RAID Methods
NOTE: Not all controllers support RAID ADG.
Item RAID 0 RAID 1+0 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 physical drives 1 2 3 4
Tolerates failure of one physical
drive? No Yes Yes Yes
Tolerates simultaneous failure of
more than one physical drive? No Only if no two
failed drives are
in the same
mirrored pair No Yes
Read performance High High High High