
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 d rives.
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)