Hardware RAID
The Pi does not have a SATA controller on board, and there is no way to attach extra hard drives except via the USB ports. The cool thing is that you can get a USB RAID controller. This makes file storage on the Pi a very attractive option. Technically, the peripheral needed is called a USB SATA multiplier.
Configuration
There is no one-step guide to configure these multipliers. Some need to be configured using software in Windows or Linux, while others may have DIP switches that configure the multiplier to a specific configuration.
Addonics is a well-known and fairly easy-to-source multiplier. You will need to search around on the Internet, online auctions, and shops for these. The prices are around the same as the Pi; but if you are looking for redundant storage, then these are the cheapest options you will find.
Massive storage
If you are looking to create a really massive storage, you can easily daisy chain a multiplier with another, sometimes up to three or four times. Recently...
