Appendix D: Understanding RAID ● 168RAID 5 Logical DrivesA RAID 5 logical drive is built from a minimum of three and amaximum of sixteen disk drives, and uses data striping and parity (seebelow) data to provide redundancy. Parity data provides dataprotection, and striping improves performance.Parity data is an error-correcting redundancy that’s used to re-createdata if a disk drive fails. In RAID 5 logical drives, parity data(represented by Ps in the example below) is striped evenly across thedisk drives with the stored data.Drive segment size is limited to the size of the smallest disk drive in thelogical drive. For instance, a logical drive with two 250 GB disk drivesand two 400 GB disk drives can contain 750 GB of stored data and 250GB of parity data, as shown below.In the example above, P represents the distributed parity data.Disk Drive 1Disk Drive 2Disk Drive 3Disk Drive 4250 GB250 GB400 GB400 GBDisk Drives in Logical DriveDisk Drive 1Disk Drive 2Disk Drive 3Disk Drive 4RAID 5 Logical Drive = 750 GB plus Parity123PNot UsedNot Used45P6 750749748P............Unused Space: 150 GBUnused Space: 150 GBDrive Segment Size (Smallest Disk Drive)
