I have been searching for a good solution for a few of my clients that have a server rack and want a simple and easy to use mirror array to use for backups. I finally stumbled upon what I think is a very good fit for what I was looking for. It is the Desert Scientific Z-Drive Rackmount Chassis.
The Z-Drive is "is a a premium drive array in a slim 1U rackmount format. Two cartridge bays are resonantly mirrored to provide constant access to data at all times." (from their website).
What I like most about this piece of hardware is that it does not require any software to run. It is pretty much just plug and play. What I also find great is that it is all steel. I have purchased many of this simple raid arrays and they are very cheaply constructed with plastic and they can not handle many hot swaps of the drives. This array is very rugged.
The price is right on this chassis. The chassis itself runs $595 and the cartridges that are either 1/2/3TB range from $295-$395.
I am very happy with this product and I will definitely be installing it for all of my clients that have a need for this.