Under the covers
Figure 19 shows a photograph of the main board on the 220.
Figure 19: NSA-220 Main Board
As far as software on the box, there are few hints found openly. A port-scan of the box turned up nothing much out of the ordinary and an attempt to fingerprint the OS was inconclusive. To try and get command-line access to the box, I broke out my usual bag of tricks such as using a argument-modifying web proxy. But this time, I was unsuccessful. ZyXEL has done a good job of locking down the user interface and filtering internally for bad input.
By examining the source to the web interface, I did find that it was written using the dojo toolkit. So my last attempt to poke at the internals was to grab a firmware image from ZyXEL and run "strings" on it. This turned up a few clues.
It showed that the box is running a Linux 2.6.12 or a 2.16.18 kernel (both strings were present in the image). There was also an indication that a serial console was present on the 220, so someone with a bit of hardware knowledge, and more time than I, could likely hook up a serial connection to get a command prompt.
Since the product is using GPL-licensed Linux, there should be source code available at the ZyXEL web site or on the CD that accompanied the product, but I couldn't find it. Hopefully, this was just an oversight by ZyXEL that will be corrected soon.
It's clear that ZyXEL put some thought and effort into the NSA220. It has solid construction, decent performance, a nice feature set and a user interface that is the best I've seen in this class of device. While I did have some small issues with the product, there were no showstoppers. The one thing I really would have liked to have seen is an email alert mechanism.
As far as a comparison to other devices in its class, the 220 stacks up pretty well, especially in comparison to the D-Link DNS-323. The 220's advantages over the 323 are primarily its jumbo frame support for improved performance, Download Service that includes Torrent support and interesting "Broadcatching" service.
The lowest price I found online was around $210, which is slightly higher than the DNS-323. Other two-drive NASes, such as the Qnap TS-209 have a larger feature set and better performance, but you'll pay in the neighborhood of $350 for them.
So as usual, you'll need to decide what's important for your intended usage. But if the NSA-220 has the features you're looking for and is in your price range, you won't go wrong in checking it out. Recommended!