That’s why I thought, using a smartphone / tablet with Android would be a nice option. These devices are not too bad …
- in terms of specs and they are pretty powerful nowadays;
- they are designed for energy efficiency;
- they are “cheap”
- bring a display for server monitoring
- the pure definition of mobility
- with uninterruptible power supply
- the I/O performance should be good enough for a “close circle” of 10-20 people and only a few at the same time.
- and of course the expendable SD card slot with 250/300 MB/s r/w speed
For what reason? External hard drives? Ethernet? I’d like to use the internal storage and SD card.
It seems to be the most convenient home server I can get, as long as the Wifi connectivity don’t drop. 
But I’ve seen ethernet adapters as well. It’s just a question of docker and ARM compatibility.
This would be a great reason to buy my first Android device 
(I’ll guess, trying to implement this on Apple devices would be much more painful).
Which one can you recommend?