I've been getting really slow transfer rates over USB 3.0 on my Sony Vaio T series Ultrabook. It has a USB 3.0 Port, I'm using a USB 3.0 hard drive with a USB 3.0 cable and all that fun stuff, too. I've updated the drivers to the latest versions for BIOS and the USB 3.0 driver as well.
The transfer rate I've seen in other threads where people complain is around 50-60. I'm getting 10-15 mb/s, which is what really bothers me. It starts off at a good rate of 80-90 for a few seconds, then just crashes down to about 30 for about a good minute or two, then goes even lower to around 15 mb/s, which I think is even slower than USB 2.0 transfer rate. Even Windows 8 shows that the hard drive is plugged into a USB 3.0 port, but not sure what else to try out. I've also tried different hard drives and different cables, as well.
HDTune shows a really high number, like around 70-90 mb/s. As time goes on, it slowly decreases, but even after like, ten minutes, it only gets to a minimum speed of around 60. The hard drives I'm using right now are a SeaGate FreeAgent GoFlex drive and a WD My Passport Portable Drive. I'll look to see how fast this is on other computers in a while, need to find another one with a USB 3.0 port first.
Well, best bet is to see what other computers do, Also, if the drive you are copying from is slow(or fragmented), but will effect the speed as well. Again those speeds DO seem slow, I will do some tests with some 5200/5400 rpm drives and see how they hold up since most portable drives are of that type.
I just did a test to show how much file size effects drives. Again, not quite for you, just extra knowledge.
Small files(to rule out the source, the small files are copied from a ramdrive) vs 1 large file Copied to a 1TB 5400rpm 2.5inch WDC blue drive
When I get a quick change, I will fire up my USB 3.0 enclosure with its BD player swapped to a hard drive to see how much the USB 3.0 interface hurts performance(after all, you have an extra chip that does not support all the features of an actual SATA controller).