Unless you're planning on installing part or all of YDL to your USB HD, it might be best to unplug it, because it's very easy to click next to check the partitioning scheme while the USB HD checkbox is checked as well as ps3sda and it does "something" to the USB HD's FAT table, without a clear warning. Don't worry, I was able to restore it, but If I had went further into the install with that checkbox check it probably would have formatted it.
Ron Rogers Jr. (CronoCloud)