Use of RAID with multiple drives
Please give me an example of when RAID 1 with multiple drives is used. I can't find a single reference to it being implemented anywhere.

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First, to clarify something, RAID 1, by definition, requires at least two disk drives. There are many vendors who support either hardware RAID via RAID adapters or external RAID arrays. There are also host-based software RAID 1 mirroring solutions with more than two drives. These solutions can enhance performance, as well as availability, and enable a drive to be taken out of a RAID set for other uses, such as a copy operation for moving data elsewhere.

If you are having challenges finding examples of multiple drive (more than two) RAID 1 implementations, try searching on "triple mirror RAID". It has been a host operating system capability for 15-17 years. Storage system vendors and even application vendors like Oracle also support triple mirror RAID. Another implementation of multiple drive RAID 1 would be a hybrid RAID 0+1 or 1+0 also known as RAID 10. This implementation works well when, for example, six disk drives are used with three each in the two unique RAID groups that are then striped or mirrored together (this depends on whether you're using 0+1 or 1+0).

Another way of finding specific implementations is to look for vendors that implement a combination of horizontal and vertical RAID. This is where one RAID group is created horizontally across a group or shelf of disk drives and the other RAID group, using perhaps a different RAID level, is created vertically across the horizontal RAID groups usually more for performance than availability.

This was first published in September 2007