HP Integrity rx4640 Server - Manual (Page 83)

Drive Arrays and Fault Tolerance
RAID ADG—Advanced Data Guarding
RAID ADG is similar to RAID 5 in that parity information is generated (and stored)
to protect against data loss caused by drive failure. With RAID ADG, however, two
different sets of parity data are used, allowing data to still be preserved if two drives
fail. As can be seen in Figure D-8, each set of parity data uses a capacity equivalent
to that of one of the constituent drives.
This method is most useful when data loss is unacceptable, but cost must also be
minimized. The probability that data loss will occur when arrays are configured with
RAID ADG is less than when they are configured with RAID 5 (for details, refer to
Appendix F).
B1
B3
P5,6
Q7,8
B2
B7
P3,4
Q5,6 B5
B8
P1,2
Q3,4 B4
B6
P7,8
Q1,2
Figure D-8: Advanced data guarding (RAID ADG)
Advantages
•
•
•
High read performance
High data availability—any two drives can fail without loss of critical data
More drive capacity usable than with RAID 1+0—parity information requires
only the storage space equivalent to two physical drives
HP Smart Array 5300 Controller User Guide D-9
HP CONFIDENTIAL
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