HP 5300 - Manual (Page 115)

Drive Arrays and Fault Tolerance
HP Smart Array 5300 Controller User Guide D-9
HP CONFIDENTIAL
Writer: Jennifer Hayward File Name: n-appd drive arrays and fault tolerance
Codename: SilverHammer Part Number: 135606-005 Last Saved On: 10/8/02 11:21 AM
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 up 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