RAID 1 ArraysA RAID 1 array is built from two disk drives, where one disk drive is a mirror of the other (the same datais stored on each disk drive). Compared to independent disk drives, RAID 1 arrays provide improvedperformance, with twice the read rate and an equal write rate of single disks. However, capacity is only50 percent of independent disk drives.If the RAID 1 array is built from different- sized disk drives, the free space, drive segment size is the sizeof the smaller disk drive, as shown in this figure.Disk Drive 2Disk Drive 1400 GBDrive Segment Size(Smallest Disk Drive)Disk Drive 1Disk Drive 2Disk Drives in Logical Drive RAID 1 Logical Drive = 250 GB1 – 2501 – 250Unused Space = 150 GB250 GBRAID 1 Enhanced ArraysA RAID 1 Enhanced (RAID 1E) array—also known as a striped mirror—is similar to a RAID 1 array exceptthat data is both mirrored and striped, and more disk drives can be included. A RAID 1E array can bebuilt from three or more disk drives.In this example, the large bold numbers represent the striped data, and the smaller, non-bold numbersrepresent the mirrored data stripes.Disk Drive 2 400 GB400 GB400 GBDisk Drive 3Disk Drive 2Disk Drive 1Disk Drive 3312645Disk Drives in Logical Drive RAID 1E Logical Drive = 600 GBDisk Drive 175Proprietary and Confidential to PMC-Sierra, Inc.Document No.: CDP-00277-02-A Rev. A, Issue:Serial Attached SCSI RAID Controllers Installation and User's Guide
