The RT1900ac has two storage ports, a USB 3.0 port and SD card slot. Both of these can be used at the same time. If you want the best performance on the USB port you are going to want to turn Interference reduction off. When we inserted our USB 3.0 drive it was automatically enabled. You can find this setting under Network Center -> Wireless -> Wi-Fi. Be sure to uncheck the box.
To test storage performance we will be using LAN Speed Test. This software easily allows us to test the speed of network-connected storage. It gives us back read and write speeds in Mbps, which we have converted to MB/s for you. Of course we will be testing both SD card and USB 3.0 performance. Our SD Card is a Kingston 16GB SDHC Class 10 card and our USB flash drive is the Patriot Magnum 2.