CertiGuide to Network+  9  Chapter 0110: Network Operating Systems (NOS)       9  IX  RAID (Server Disk Arrays)

RAID 0 1 RAID 5

RAID 1 is also known as disk mirroring. Whenever data is written to one drive, the second drive gets an exact copy of the data.

The good news is that one drive can totally fail, and an exact copy is still available on the still functioning drive. The down side is that in terms of investment, this form of RAID has the highest investment, since everything is written twice.

Data reading is faster than a single drive; however writing data can actually be slower, since it all must happen twice.

A point of failure not handled in mirroring drives is that of a controller failure. In the rare event of a controller failure, one of two things happens. The controller slips into death quietly, and both drives cease to function until the controller is replaced.

The other scenario involved a drive controller displaying its protest on entering the death stage. In this event, it may scramble the data, leaving both drives with useless information.

The solution to this type of event is to use a modified form of disk mirroring known as disk duplexing. This technique adds a second controller to the disk array so a failure of either one drive or controller does not compromise data integrity.

RAID 0 1 RAID 5