Thanks for pointing that out.
I do see that the file locations are diff from the library location. So you do use NAS (Network) and not attached HD (USB)?
I use a homemade NAS on a Gb switch for data rather than local storage (but to be clear I keep the library database on an internal SSD).
My personal experience has been that USB spinning disk hard drives (HDDs) are significantly slower and more failure prone than conventional internal HDDs, so I try to avoid USB drives whenever possible.
As for NAS vs. USB, in terms of speed, USB3 is theoretically faster than an ethernet connection if the drive supports it, but most HDD's have a max read speed in the 80-100MB/s range. That won't saturate a Gb ethernet connection, so there isn't even a theoretical speed advantage to USB3 for most HDDs. And networked storage makes the data accessible all over the house without having to leave a power-hungry PC on, which is also nice.
Two Caveats:
1) If you can't wire up a hypothetical NAS, I'd be more inclined to look back into local storage. WiFi (even newish AC WiFi) kind of sucks if you need significant bandwidth (like for HD video). The router manufacturers quote ridiculous bandwidth stats, but they're not really achievable in most real world conditions.
2) If you only have one PC that will use the data, local storage probably makes the most sense from a power consumption standpoint (and cost, and ease of use, and ...), but internal drives are preferable to USB (both for speed and reliability) if you can get a good price on the big ones.