Appendix C: Selecting the Best RAID Level ● 163RAID 5 Logical DrivesA RAID 5 logical drive is built from a minimum of three disk drives, and uses data striping andparity data to provide redundancy. Parity data provides data protection, and striping improvesperformance.Parity data is an error-correcting redundancy that’s used to re-create data if a disk drive fails.In RAID 5 logical drives, parity data (represented by Ps in the next figure) is striped evenlyacross the disk drives with the stored data.Drive segment size is limited to the size of the smallest disk drive in the logical drive. Forinstance, a logical drive with two 250 GB disk drives and two 400 GB disk drives can contain750 GB of stored data and 250 GB of parity data, as shown in this figure.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 4 ... P2 5 ... 7483 P ... 749P 6 ... 750Unused Space = 150 GBDisk Drives in Logical DriveUnused Space = 150 GB= 750 GB plus Parity and SpareRAID 5Logical Drive
