Adaptec 2420SA User Guide - Page 73
RAID 5 Arrays, disk drives with the stored data.
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Appendix B: Understanding RAID ● 73 RAID 5 Arrays A RAID 5 array is built from a minimum of three disk drives, and uses data striping and parity data to provide redundancy. Parity data provides data protection, and striping improves performance. Parity data is an error-correcting redundancy that's used to re-create data if a disk drive fails. In RAID 5 arrays, parity data (represented by Ps in the next figure) is striped evenly across the disk drives with the stored data. Drive segment size is limited to the size of the smallest disk drive in the array. For instance, an array with two 250 GB disk drives and two 400 GB disk drives can contain 750 GB of stored data and 250 GB of parity data, as shown in this figure. 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 4 ... P Disk Drive 2 2 5 ... 748 Disk Drive 3 3 P ... 749 Unused Space = 150 GB Disk Drive 4 P 6 ... 750 Unused Space = 150 GB RAID 5 Logical Drive = 750 GB plus Parity