Advanced Data Guarding User Guide

Compaq Confidential – Need to Know Required

Writer: John Turner Project: Advanced Data Guarding for the Smart Array 5300 Controller Reference Guide Comments: final draft

Part Number: 188270-xx1 File Name: b-ch1 RAID ADG.doc Last Saved On: 12/11/00 12:04 PM

Chapter

Introduction: RAID ADG

RAID ADG is similar to RAID 5 in that data protection is achieved by writing

parity information to the physical drives in the array. With RAID ADG,

however, two sets of parity data are used (Figure 1-1). These two sets are

different, and each set occupies a capacity equivalent to that of one of the

constituent drives. (For further information about other RAID levels, refer to

the Compaq Smart Array 5300 Controller User Guide.)

P5,6

P7,8

P3,4

P5,6

P3,4

P1,2

P7,8

Figure 1-1. RAID ADG, showing data blocks (B) and two sets of parity data (P)

RAID ADG is most useful when data loss cannot be accepted, but low cost of

implementation is also desirable. The probability that a system will suffer data

loss when configured with RAID ADG is less than when configured with

either RAID 1 or RAID 5 (see Appendix C for reliability data).