Adaptec 5405 User Guide - Page 155
RAID 1 Logical Drives, a RAID 1 logical drive except that data is both mirrored
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Appendix B: Selecting the Best RAID Level ● 155 RAID 1 Logical Drives A RAID 1 logical drive is built from two disk drives, where one disk drive is a mirror of the other (the same data is stored on each disk drive). Compared to independent disk drives, RAID 1 logical drives provide 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 logical drive is built from different-sized disk drives, drive segment size is the size of the smaller disk drive, as shown in this figure. Drive Segment Size (Smallest Disk Drive) Disk Drive 1 250 GB Disk Drive 2 400 GB Disk Drives in Logical Drive Disk Drive 1 1 - 250 Disk Drive 2 1 - 250 Unused Space = 150 GB RAID 1 Logical Drive = 250 GB RAID 1 Enhanced Logical Drives A RAID 1 Enhanced (RAID 1E) logical drive-also referred to as a striped mirror-is similar to a RAID 1 logical drive except that data is both mirrored and striped, and more disk drives can be included. A RAID 1E logical drive can be built from three or more disk drives. In this figure, the large bold numbers represent the striped data, and the smaller, non-bold numbers represent the mirrored data stripes. Disk Drive 1 400 GB Disk Drive 2 400 GB Disk Drive 3 400 GB Disk Drives in Logical Drive Disk Drive 1 1 3 4 6 Disk Drive 2 2 1 5 4 Disk Drive 3 3 2 6 5 RAID 1E Logical Drive = 600 GB