BW,
The Terastation Pro's compatible with the "power bad" signal put out by UPSes by APC and Omron. The smallest UPS is all you need since a 350W unit could power the TS for 5 minutes, and you just need 1 minute: USB cable from the UPS to the Terastation, and the unit shuts down nicely when the power goes out. Or you could configure it to wait for the USP "battery low" signal, but I'm not brave enough to test that on a small UPS
. UPS was less than $100. You need to check exactly which models work, there are exceptions.