When I had my setup with an ASUS EEE PC I had mobile external HDDs plugged to it via USB.

Since my use case was long-term storage and feeding video files to a Media TV Box, the bandwidth limit of USB 2.0 and using HDDs rather than SDDs was fine. Also back then I had 100Mbps ethernet so that too limited bandwidth.

Even in my current setup where I use a Mini-PC to do the same, I still have the storage be external mobile HDDs and now badwidth limits are 1Gbps ethernet and USB 3.0, which is still fine for my use case.

Because my use case now is long term storage, home file sharing and torrenting, my home network is using the same principles as distributed systems and modern microprocessor architectures: smaller faster data stores with often used data close to were its used (for example fast smaller SDDs with the OS and game executables inside my gaming machine, plus a torrent server inside that same Mini-PC using its internal SDD) and then layered outwards with decreasing speed and increasing size (that same desktop machine has an internal "storage" HDD filled with low use files, and one network hop from it there's the Mini-PC NAS sharing its external HDDs containing longer term storage files).

The whole thing tries to balance storage costs and with usage needs.

I suppose I could improve performance a bit more by setting up some of the space in the internal SDD in the Mini-PC as a read/write cache for the external HDDs, but so far I haven't had the patience to do it.

I used to design high performance distributed computing systems and funnilly enough my home setup follows the same design principles (which I had not noticed until thinking about it now as I wrote this).