Why is my USB3 speed slow ?

Question

I have a T450s with a 500 gb Samsung SSD as the hard drive. I recently bought the WD 4TB USB3.0 and started copying data from hard disk to the the external WD. All usb ports on laptop are 3.0. But the average copying speed runs between 60 - 109 mb/s. I thought with a usb 3, we should run into gbps as the average read/write copy speed . What am i missing?

Answer 1

"I thought with a usb 3, we should run into gbps as the average read/write copy speed . "



LOL, nope, not even remotely close. With USB 3 and a mechanical HDD 60-109 MB/S is what you can realistically expect. When I do my bi-annual backup to my external HDD (it has a 4TB WD Black inside of it) with USB 3 I get 70-120 MB/S which is similar to what you're getting.

Answer 2

You are mistaking Max speed, for Average speed.

Answer 3

What kind of drive is in your external drive? If it's a mechanical one it would probably be the limiting factor.

Answer 4

USB is a serial data link and it's internal data speeds are given in bits per second, as with network links, SATA etc.



It's raw data rate is 5Gbit/sec

That equates to 640MBytes per second.



However, your 4TB USB3 drive uses a mechanical hard drive which is vastly slower than that, so it's the drive that sets the overall speed.



The "weakest link" is the controlling factor.



Also, when copying random-size files, the Windows file system has to keep creating and updating the directories on the drive which causes a pause in the overall copy every time the drive head has to seek back to the directory area. Lots of small files can slow a copy to a crawl even with fast drives.