6 Reasons Why your Flash Drive is Slow

Wondering why your flash drive is so slow even you’ve already plugged it into USB 3.0 port?  In this post we’ll talk about 6 reasons that could make your Flash drive transfer speed slow.

Thermal Throttle

Transferring lots of data generates heat. After using your flash drive for a while it will heat up to the point that the controller has to reduce the data transfer in order to cool down. We call this “Thermal Throttle” We usually find this problem with a small flash drive with plastic body which heat can disperse poorly. If you notice a slow transfer speed then try touching it to see if it’s hot.


If this is indeed the problem then there is nothing we can really do since it’s a design flaw. When you buy a new flash drive next time, try to look for one with aluminum body.

Too Many Files

Transferring 100MB file and 100 of 1MB files is not the same. Transferring multiple files is very much slower due to lots of overhead. If you’re copying the entire folders to Flash Drive then you should try zipping it as one big file.



Theoretically USB Hub shouldn’t slow down the transfer rate. However, we usually see slower speed or even file corruption when Flash Drive is plugged into USB Hub (especially a cheap one!) Try using your Motherboard’s USB 3.0 port when possible.


Moreover, USB Hub shared bandwidth among all devices currently plugged in. So if you have multiple devices on that hub then you shouldn’t be surprise if it’s slow.

Transferring Large File

The transferring speed advertised for your Flash Drive is usually the theoretically maximum speed (notice the word “Up to“) When you start copying the file, you’ll notice a sudden burst of speed. This because of the writing cache/buffer. But if the file is large (more than 1-2GB) The cache will be filled up and the speed will drop down as the flash drive controller can’t keep up. They will even drop from MB/s to KB/s rate after a while, and then go back up, and then drop down again.


To test this, I use CrystalDiskMark to compare between 100MB and 2GB file size speed. The result is larger file is more than 2x slower!! (48MB/s vs 17.96MB/s)



Slow Harddisk Speed

If you’re copying file from harddisk to your flash drive, it’s possible that the harddisk speed can’t keep up with the Flash drive speed. Especially, if you’re using entry level laptop without SSD. Physical harddrive can have fragmentation issue which cause slow access to the file. Try transferring file from faster PC that has SSD to identify the issue.

Low Quality Flash Drive

Cheap flash drives use low quality component. Flash drive controller needs to process large amount of data during the transfer. Low quality NAND chip and controller need to read and write at a slower rate to avoid errors (or it will corrupt the data) Good, fast and cheap can’t co-existed together. If possible, don’t buy the lowest price series and aim for a performance one.


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