The purpose of RAID is NOT backup. The primary goal of RAID is to provide Fault Tolerance and a)redundancy (mirroring), and b)increased performance (striping a single logical drive volume across multiple physical drives), by designating one or more parity drives to striped components. The whole point is to minimize downtime and keep data accessible. This is not a backup strategy, but a part of one.

In a quality external RAID box, not only are there redundant drives, but the box will also have redundant power supplies, I/O ports, etc to insure against data loss. When multiple I/0 ethernet ports are provided, the custom is to do port aggregation - where multiple ports are ganged together to provide a wider data path and faster I/O. All of these things, are hot swappable ie you don't have to shut down the appliance to replace failed components. Mirroring is an extremely inefficient use of multiple drives - but it is pretty safe. I use RAID 1+0 which is mirroring AND striping, for faster read-writes.

The scalability of RAID makes it ideal when you need to add capacity. You don't even have to shut down the system or copy things from one drive to another to increase capacity in a properly implemented array.

For a business network, you need something like RAID. I set it up in my business. However, for home use, I wonder how necessary it really is. We want to back up several things: the operating system, programs, program settings and, finally, data. You can do this without RAID but is more difficult and time-consuming to restore. Fortunately, we today's drives, we do not have the problems from years ago.

To answer my own question, you should probably use RAID at home. My problem is that I already have too many drives in my machine.