In our recent review of Intel's "Next Unit of Computing" barebones box, we explained a snafu we encountered with large network file transfers causing the system to lock up. At the time, we were working with Intel on resolving the problem and suspected it was confined to our particular review unit. After further testing, we have a clearer sense of the nature of the problem, and potential NUC buyers should read carefully from here.
First, our own testing has convinced us that this issue is indeed thermal in nature. The system usually locks up somewhere before reaching the 5GB mark in a large network file transfer. However, we were able to eliminate the lock-ups, to the point where we succeeded in transfering over 40GB without issue, by doing either of two things: 1) removing the cover of the device, exposing the closely-sandwiched Wi-Fi NIC and SSD cards to open air, or 2) changing the system cooling policy in the BIOS to run the fan at 100% speed constantly.
Neither of these measures is a true remedy, of course. You're going to want to have the case screwed together when using the system, and the usually silent NUC is much, much louder and rather annoying when its fan is running at its peak speed. Still, the fact that these measures stabilize the system confirms that the problem is thermal, in our view.
We continue to believe the Wi-Fi card is heating up, causing the SSD situated alongside it to overheat and become unresponsive.
Next, Intel informs us that it has now reproduced the network file transfer problem in its own labs when the DC3217BY model NUC is equipped with the exact same Wi-Fi and SSD cards that we used in our testing. (Both of these mini-PCIe cards are Intel products, supplied to us alongside the NUC for use in our review.) Apparently, reproducing the issue took longer than expected because Intel's initial tests didn't duplicate our hardware config exactly. We understand the problem doesn't appear when the NUC is equipped with a Gen 2 mSATA device, only Gen 3.
The other NUC model, the DC3217IYE with Gigabit Ethernet rather than Thunderbolt, apparently isn't affected by this problem.
Intel tell us it's working on a fix, potentially via a BIOS update. We're rooting for them to succeed, but we have our reservations. If the issue is entirely thermal in nature, then the design of the NUC system and enclosure may make a true fix difficult to implement via software. The NUC's thermal solution is on the other side of the motherboard from the Wi-Fi and SSD cards, since it's primarily intended to cool the CPU and the platform controller hub chip. An especially aggressive fan speed profile might drastically reduce or eliminate lock-ups, but it could also transform an unobtrusive, virtually silent system into a fairly noisy affair—unacceptable for this sort of product, in our view.
Intel may very well resolve the problem without compromising the NUC's acoustics, so don't make too much of our worries just yet. We simply recommend waiting until we can confirm that Intel has fixed the problem via a BIOS update before buying a BY-model NUC. We'll keep you posted as we learn more.