Drop in read performance during benchmark

Hi everyone,

Could anyone point me to the direction, explaining the sudden drop in read performance during standard Ubuntu Disk benchmark after a certain time?

Is it the USB drive fault? Why the write performance doesn’t suffer then? Is it the system? What part exactly? Is it the benchmark itself? What is the correct one then?

Screenshot from 2017-05-09 19-40-05.png

Screenshot from 2017-05-09 20-18-22.png


EDIT: Forgot the details, that is SanDisk Extreme Go 64GB, Lenovo T450s and Ubuntu 17.04

Here is the result from another Lenovo laptop running Windows, using HD Tach 2.55 with 1Mb samples:


So apparently, the key to this behaviour in the USB Flash Drive itself, although the chart looks different, but similar way too much.

The main question now is whether it’s a defect, or can anything be done to fix it?