Terastation WS5420DN

Stock Firmware Installation
The device comes with Windows Storage Server installed and can be recovered via the included SD card.

Custom Firmware/Operating System installation
These devices run on an Intel Atom processor with a fairly typical BIOS and include a VGA out and support USB keyboards, you should be able to run virtually any operating system that will run on a normal PC depending on drivers/etc.

For tools to help install and configure Debian on these devices, see Installing Debian on Intel Terastations

Buffalo Resources

 * Manuals, Firmware, etc