RAID Terminology
Disk Striping
Disk striping allows you to write data across multiple physical disks instead of just one physical disk. Disk striping involves partitioning each physical disk storage space into stripes of the various sizes. These stripes are interleaved in a repeated sequential manner. The part of the stripe on a single physical disk is called a stripe element.
For example, in a
Figure 2-1 shows an example of disk striping.
Figure 2-1. Example of Disk Striping (RAID 0)
Stripe element 1 Stripe element 5 Stripe element 9
Stripe element 2 Stripe element 6 Stripe element 10
Stripe element 3 Stripe element 7 Stripe element 11
Stripe element 4 Stripe element 8 Stripe element 12
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 rebuild the failed physical disk. The primary advantage of disk mirroring is that it provides 100 percent 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 a copy of the same data at all times. Either of the physical disks can act as the operational physical disk. Disk mirroring provides 100 percent redundancy, but is expensive because each physical disk in the system must be duplicated.
Figure 2-2 shows an example of disk mirroring.
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