This issue made my DNS-321 almost useless to me. This issue was reported 16 months ago. I started complaining about it 10 months ago. I was active on the forums. I even wrote a personal letter to the D-Link office. (Yes, developers, you pissed me off that much.)
Now, I just ditched my DNS-321 for a Synology DS209. Hallelujah! Here's my review:
Even though I am right with ya on the issue of very disappointing "gigabit speed" file transfers, I do have to make one point here for Dlink. The Synology unit may be much faster, but maybe that is because it is MUCH more expensive. My supplier's retail price on a DNS-321 is around $149 when it's not on sale for $119, which is quite often. The Synology DS209 lists for around $340 and I have almost never seen it on sale.
When you look at your upload speed difference being just over 2x faster, and your download speed being 3x faster, then look at the price being just under 3x more, I guess it's all relative eh?

But truly, I do wish Dlink would either fix the gigabit problem or else stop advertising both units, 321 and 323, as being gigabit boxes, it is very misleading advertising. I bought them for storage, but that was one of my influencing factors when I decided on Dlink, the fact that I could have a "gigabit unit" for such a low price! I still like both of my units, but this missing feature has made it harder to recommend them to others who want a unit with decent speed.
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Ryder