The USB socket on the older streamers was provided to allow an iPhone to be connected. You can sometimes get small USB sticks to connect, but it’s not easy to find ones that work.
So the answer is that you can’t really expect to connect a USB hard drive to the USB socket on an ND5 XS.
USB playback on 1st gen streamers is officially supported and it should work, but the basic folder view is best suited to relatively small libraries and it’s expected that USB memory sticks are used.
The port provides power for the drive: don’t attempt to use an externally powered drive of a spinning HDD. A correctly formatted USB stick should be fine.
I found that spinning hard drives would sometimes work, but not always, whereas I never had a problem with memory sticks, even relatively large capacity ones.
If you’re otherwise happy with your ND5XS a better option might be to buy a NAS and use UPnP, which is what 1st gen streamers were primarily designed for. Otherwise an ND5XS2 has plenty of advantages over it’s predecessor.
How large is your music library? Even with a 2nd gen streamers you may find that a NAS is more versatile than a USB drive.