Đồng thời, bộ điều khiển RAID tính toán thông tin chẵn lẻ và lưu trữ nó trên đĩa còn lại. Kết quả là rằng, nếu một đĩa bị mất, dữ liệu trên đĩa đó có thể được tái tạo bằng cách so sánh các dữ liệu trên các đĩa còn sống sót và thông tin chẵn lẻ. (RAID 5, thông tin tính chẵn lẻ được phân phối qua các đĩa, để các nội dung của bất kỳ đĩa nào | 48 Chapter 2 Designing and Planning Server High Availability RAID 5 offers a balance of performance and fault tolerance by implementing a stripe set improved performance with a parity check redundancy . RAID 5 which requires at least three physical disks splits the write operation across n-1 disks that is if you have five disks the write operation is split across four of the disks to improve performance. At the same time the RAID controller calculates parity information and stores it on the remaining disk. The result is that if a disk is lost the data on that disk can be re-created by comparing the data on the surviving disks and the parity information. In RAID 5 the parity information is distributed among the disks so that the contents of any given disk are 1 n parity info and n-1 n actual data. Using a parity disk means lower cost per storage unit with RAID 5 you lose only 1 n of the storage space you bought as opposed to half with RAID 1 but the performance gain of striping is partially offset by the calculation of the parity information. Thus RAID 5 doesn t offer quite the performance increase that RAID 0 does but it does offer some write improvement along with redundancy not offered by RAID 0. RAID 0 1 sometimes called RAID 10 offers both the performance increase of RAID 0 striping and the redundancy of RAID 1. In RAID 10 you build a RAID 0 stripe set and then implement a RAID 1 mirror of the entire stripe set. Because the RAID controller isn t calculating parity data the RAID 1 mirror doesn t introduce an offsetting performance decrease in offering the redundancy. However as with any RAID 1 implementation RAID 10 uses half the storage space purchased for redundancy so only half of what you bough appears useable. Also because a RAID 0 stripe set requires at least two disks and because a RAID 0 mirror doubles the disk requirements a RAID 10 set requires a minimum of four physical disks. Thus RAID 10 is the more expensive than the other RAID levels we ve .
