I'm transferring a handful of files from an internal HDD to an external HDD over USB3.0, but find that I'm getting nowhere near USB3 speeds.

The drive is definitely USB3 (Seagate STEB6000403) and plugged in correctly, I've run HD Tune and it gets roughly 150MB/s on the file write benchmark. If I copy files from the internal SSD, they transfer to it at about 130MB/s so the USB3 is working correctly.

When I start the copy from the HDD, the transfer goes fast for about a minute or so then drops to fluctuate between 20MB/s and 50MB/s. I assume it's fast because of some sort of write cache? If I plug the drive in over USB2, I get a pretty consistent 30MB/s at all times.

The drive is very full and it's a WD Green, but I would've thought it would still be able to achieve higher than 30MB/s. Even when copying things from the HDD to the internal SSD, it stays at about 70. Running the HD Tune benchmark reports a average of ~140MB/s read. Makes it seem like the slow speeds are specifically between the USB drive and the internal one, as they're both much faster trying to transfer to anywhere else.


  • How many is a handful? How big are the files? What is the total size of all the files? What if you copy the files onto the same drive, how fast is that? – Nelson Jul 21 '18 at 10:37
  • If your source drive is full with "handful of files", it is very likely that it is heavily fragmented. It could be that the copy routine starts from a handful of unfragmented files, and hits a bunch of heavily fragmented files, and transfer speed crawls down. – Ale..chenski Jul 23 '18 at 0:28
  • Did you ever solve your problem? I seem to have a similar one: superuser.com/questions/1380168/… – Nameless Dec 2 '18 at 18:04

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