Why such a low USB speed EA6200?

Hi all.
I recently purchased my ea6200, and have set up a hard drive on the router.

I have only 4 MB/s r/w speed with firmware version 1.1.41.162599
And only 8 MB/s r/w speed with default firmware version

Why? My USB hard drive up to 100 MB/s read speed. EA6200 has a USB 3.0.
And why after the update speed dropped another 2 times?