Why does the write speed on an external drive drop?

Question

USB

Completely new computer, gaming board. I connect an external drive (box on usb3.0, ssd inside). First, the file is transferred to an external drive with a maximum speed of 300 mb / s, but after, somewhere in the middle of the recording, it steadily decreases to 40 mb / s. What could be the problem here?

Answer 1

Apparently, the cache has filled up on the external disk, and now the recording starts at the speed of the disk.