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Appendix D: Understanding RAID ● 165
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, the
free space, drive segment size is the size of the smaller disk drive, as
shown below.
D
isk Drive 1
D
isk 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 G
B
1 – 250
1 – 250
Drive Segment Size (Smaller Disk Drive)