OpenWrt usb flash drive backup:

Create backup:
sudo tar -C /media/openwrt-data --exclude=.transmission --exclude=.mpd.database --exclude=lost+found -zcf openwrt-data.tar.gz .
sudo tar -C /media/openwrt-root --exclude=lost+found -zcf openwrt-root.tar.gz .

Extract backup:
sudo tar -C /media/openwrt-root -zxf openwrt-root.tar.gz
sudo tar -C /media/openwrt-data -zxf openwrt-data.tar.gz