This post I expect OpenWrt has been installed, if not please refer my previous post. The full documentation about Extroot can be found from this link http://wiki.openwrt.org/doc/howto/extroot .
The step showed here is the working implementation on TP-Link MR3020 using the following environment.
Firmware Version: OpenWrt Attitude Adjustment 12.09
1. USB 2.0 Hub
2. USB 2.0 Flash Drive (~8GB)
3. ZTE MF-190 3G Modem
