HP Integrity rx4640 Server - Manual (Page 84)

Drive Arrays and Fault Tolerance
Disadvantage
The only significant 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 Hardware-Based RAID Methods
Table D-1 summarizes the important features of the different kinds of RAID methods
described here. The decision chart in Table D-2 may help you to determine which
option is best for your situation.
Table D-1: Summary of RAID Methods
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 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: (1) All physical drives in the
array have the same capacity; (2) Online spares are not used; (3) No more than 14 physical drives
are used per array for RAID 5; (4) No more than 56 drives are used with RAID ADG.
D-10 HP Smart Array 5300 Controller User Guide
HP CONFIDENTIAL
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