[jll29]

I recommend a 19" Rack (e.g. 2x 1U) with sufficient bays - i.e. 4 or more - (1) so that you can set up a RAID array [1]; and (2) also consider building one NAS for fast access (SSDs, no RAID) and another, larger NAS for protecting against longer-term data loss (HDDs, RAID6). [No, that is not called a "backup", because backups are offsite by definition!]

Synology has perhaps the best usability (my preference, I use a RS422+ on a separate network - internal only - at home and another Synology rack version at work), and QNAP has a slight price advantage (most colleagues' preference). Synology's system software logs a warning if non-synology drives are used, but this is likely just a marketing thing; what is important is that you use "enterprise class" drives for longest lifetime (I don't save on protecting my life's data).

A 19" rack needs space, but the main problem is the generated noise (lucky if you have a room in the basement). I also have several servers, some are more power-hungry than others; one is a specific low-noise, low-energy one that is quite old, but not used as a NAS at the moment.

Many people have experimented with RasPI-based NAS, but for me that does not work as I need a solid, closed case with a more powerful CPU and professional heat management.

[1] https://en.wikipedia.org/wiki/Standard_RAID_levels