Appendix B: Understanding RAID
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81
RAID 1 Arrays
A RAID 1 array 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 arrays 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 array is built from different- sized disk drives, the free
space, drive segment size is the size of the smaller disk drive, as shown
below.
Disk Drive 1
Disk Drive 2
250 GB
400 GB
Disk Drives in Logical Drive
Disk Drive 1
Disk Drive 2
RAID 1 Logical Drive = 250 GB
Not Used
Unused Space: 150 GB
1 – 250
1 – 250
Drive Segment Size (Smaller Disk Drive)
