We use a Thecus N2050 at work for external backups. The Thecus had been running very well (albeit noisily) in a hosted data-center environment, but has recently been shifted to our local office.
Now, a couple of days ago, the Thecus (as we like to call it) started to have some serious issues - spefically, our Linux kernel was reporting constant IO errors whenever the device was under heavy use. After a quick check, I noticed that the lights on the front were flashing to indicate that the second disk had failed. Since the device was (and still is) running in RAID 1, this should not have affected the device's reliability, but just to sure, I pulled the second disk out.
It was then, upon restarting the Thecus with one less disk, that I noticed the horribly loud fan... and subsequently realised, that the fan could not have been working prior, since it was so obvious now! :(