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34 Introduction to RAID
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Disk Mirroring
With mirroring (used in RAID 1), data written to one disk is simultaneously
written to another disk. If one disk fails, the contents of the other disk can
be used to run the system and reconstruct the failed disk. The primary
advantage of disk mirroring is that it provides 100% data redundancy.
Because the contents of the disk are completely written to a second disk, it
does not matter if one of the disks fails. Both disks contain the same data at
all times. Either drive can act as the operational drive.
Disk mirroring provides 100% redundancy, but is expensive because each
drive in the system must be duplicated.
Figure 2-2. Example of Disk Mirroring
Segment 1
Segment 2
Segment 3
Segment 1 Duplicated
Segment 2 Duplicated
Segment 3 Duplicated
Segment 4 Segment 4 Duplicated