Appendix B: Understanding RAID ● 60RAID 1 ArraysA RAID 1 array is built from two disk drives, where one disk drive is a mirror of the other (thesame data is stored on each disk drive). Compared to independent disk drives, RAID 1 arraysprovide improved performance, with twice the read rate and an equal write rate of single disks.However, capacity is only 50 percent of independent disk drives.If the RAID 1 array is built from different-sized disk drives, the free space, drive segment size isthe size of the smaller disk drive, as shown in the following figure.RAID 10 ArraysA RAID 10 array is built from two or more equal-sized RAID 1 arrays. Adaptec RAIDcontrollers support a maximum number of 48 disk drives in a RAID 10 array.Data in a RAID 10 array is both striped and mirrored. Mirroring provides data protection, andstriping improves performance.Drive segment size is limited to the size of the smallest disk drive in the array. For instance, anarray with two 250 GB disk drives and two 400 GB disk drives can create two mirrored drivesegments of 250 GB, for a total of 500 GB for the array, as shown in the following figure.Disk Drive 1Disk Drive 2250 GB400 GBDisk Drives in Logical DriveDisk Drive 1Disk Drive 2RAID 1 Logical Drive = 250 GBNot Used Unused Space: 150 GB1 – 2501 – 250Drive Segment Size (Smaller Disk Drive)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 10 Logical Drive = 500 GB1212Not UsedNot Used3434 500499500499............Unused Space: 150 GBUnused Space: 150 GBDrive Segment Size (Smallest Disk Drive)
