Slow Read Speeds on External Hard Disk

I have a strange issue on my OpenWrt 18.06.2, where I have connected an external hard disk via USB. I have good write speeds via samba and rsync (4MB/s or 32Mb/s), whereas I only get around 300KB/s or 2.34Mb/s read speeds using samba and rsync. I have done HDD read and write speeds using dd and I get around 6MB/s read speed and over 4MB/s write speed. Please help.

Which router?

First guess is underpowered SoC

The description of cases you compared was difficult for me to understand.

My router is a Xiaomi MiWifi Mini. The strange issue here is that the write speeds are far higher whereas read speeds are lower, and this happens with both samba and rsync.

I’m still not sure what you’re measuring and how, but slowdown when running complex applications like samba and rsync are often caused by CPU limits.

I am simply copying a file from the router to my laptop via samba. The speed shown by Windows copy dialog is 300KB/s.

However, if I copy a file from my laptop to the router, I get 4MB/s speed.

Anybody here to help?