Adaptec 2820SA User Guide - Page 73

Appendix B: Understanding RAID ● 73 RAID 6 Arrays A RAID 6 array-also known as dual drive failure protection-is similar to a RAID 5 array because it uses data striping and parity data to provide redundancy. However, RAID 6 arrays include two independent sets of parity data instead of one. Both sets of parity data are striped separately across all disk drives in the array. RAID 6 arrays provide extra protection for your data because they can recover from two simultaneous disk drive failures. However, the extra parity calculation slows performance (compared to RAID 5 arrays). RAID 6 arrays must be built from four or more disk drives, to a maximum of sixteen. Maximum stripe size depends on the number of disk drives in the array. Disk Drive 1 250 GB Drive Segment Size (Smallest Disk Drive) Disk Drive 2 250 GB Disk Drive 3 400 GB Disk Drive 4 400 GB Disk Drives in Logical Drive Disk Drive 1 1 P1 ... P2 Disk Drive 2 2 P2 ... 449 Disk Drive 3 P1 3 ... P1 Unused Space = 150 GB Disk Drive 4 P2 4 ... 500 Unused Space = 150 GB RAID 6 Logical Drive = 750 GB plus Parity (P1 & P2) RAID 60 Arrays Similar to a RAID 50 array (see page 72), a RAID 60 array-also known as dual drive failure protection-is built from eight disk drives configured as two or more RAID 6 arrays, and stripes stored data and two sets of parity data across all disk drives in both RAID 6 arrays. Note: Because the Adaptec 2420SA RAID controller doesn't support more than four disk drives, it doesn't support RAID 60 arrays. Two sets of parity data provide enhanced data protection, and striping improves performance. RAID 60 arrays also provide high data transfer speeds.