Appendix B: Understanding RAID ● 81RAID 6 ArraysA RAID 6 array—also known as dual drive failure protection—is similar to a RAID 5 arraybecause it uses data striping and parity data to provide redundancy. However, RAID 6 arraysinclude two independent sets of parity data instead of one. Both sets of parity data are stripedseparately across all disk drives in the array.RAID 6 arrays provide extra protection for your data because they can recover from twosimultaneous disk drive failures. However, the extra parity calculation slows performance(compared to RAID 5 arrays).RAID 6 arrays must be built from at least four disk drives. Maximum stripe size depends onthe number of disk drives in the array.RAID 60 ArraysSimilar to a RAID 50 array (see page 80), a RAID 60 array—also known as dual drive failureprotection—is built from eight disk drives configured as two or more RAID 6 arrays, andstripes stored data and two sets of parity data across all disk drives in both RAID 6 arrays.Two sets of parity data provide enhanced data protection, and striping improves performance.RAID 60 arrays also provide high data transfer speeds.Disk Drive 1Disk Drive 2Disk Drive 3Disk Drive 4250 GB250 GB400 GB400 GBDrive Segment Size(Smallest Disk Drive)Disk Drive 2Disk Drive 3Disk Drive 4Disk Drive 11 P1 ... P22 P2 ... 449P1 3 ... P1P2 4 ... 500Unused Space = 150 GBDisk Drives in Logical Drive Based on the drive segment sizes used:RAID 6 Logical Drive = 500 GB plusparity (P1 & P2)Unused Space = 150 GB
