One of my USB flash drive (Sandisk 256 GB USB 3.0) is showing quite irregular transfer speeds for larger files (~4GB per file), on my Surface Pro 6. There are no other resource-intensive processes running, and the machine is plugged in. Both the USB flash drive and the Surface's SSD are NTFS formatted.

I am wondering, what could be potential reasons for this behaviour, and are there ways to fix this? Defrag? Driver Update? Shorter File Names? Other performance settings?

These are graphs for one individual 4GB file each:

88% complete.

77% complete.


Such fluctuations in copy speeds are very normal.

If you have a lot of small files that are copied,

the copy speed will go down.

View the example below.

enter image description here

Whenever I make a backup of the video game I am currently working on,

the copy speed drops from around 75 MB/s to 3 MB/s (sometimes even lower),

when a large amount of small .wav files are copied.

This happens on every external hard drive that I use, mostly WD Elements.

You could use Fast Copy to increase the speed.

  • This might be true, but in the case of USB flash drives, I believe the issue might also be allocation of sectors. For example, I copied a 3GB file yesterday onto a Kingston USB 3.0 flash drive and the speed was abysmal. But then today—after cleaning off about 20GB of space on the flash drive—the copy speed was noticeably faster. – JakeGould Jul 24 at 23:22
  • That's right, the amount of data on a disc can also determine the speed. – Dr RedAnt Jul 24 at 23:30
  • @DrRedAnt I know that this is the case with loads of small files. But my question was specifically about copying larger files. – Phil-ZXX Jul 26 at 16:08

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