Thank you all for the hints, so far it was all very helpful to me, yet I will comment only about what I don't like at each method, so please don't get mad at me for talking only about the bad parts:
1.
rsync - got very bad memories from the first time I tried to use it (used the wrong combination of switches and ended up deleting the file server according to my almost empty local folder
![Grin ;D](https://www.eevblog.com/forum/Smileys/default/grin.gif)
). All my fault, of course, but since then I avoid it.
If I understood correctly, rsync does not keep an incremental backup, so it can not restore deleted or former version of files. Is this true?
2.
Nextcloud - took a look at it, and it's good that it's free and open source, but I never need a web interface to my files, never open the projects other than from a mounted location on a local desktop. I am trying to stay away of 3rd party turnkey solutions because they tend to lock the user into a certain environment then they become discontinued.
3.
Rsnapshot/back in time/timeshift will read about them, too. Would be very nice if the backup stays reasonably small. For example 1 TB occupied instead of 0.1 TB current size for a "write only" like style of backup, so I can access files deleted last year, would be great.
4.
OpenZFS for the NAS and use the ZFS
send/receive seems very tempting, yet the NAS is a "WD ShareSpace" dedicated single board computer, and most probably not a 386 architecture):
http://products.wdc.com/library/UM/ENG/4779-705006.pdfI am not sure if is it possible to install OpenZFS on the WD ShareSpace hardware, and I suspect the hardware doesn't have much RAM either.
Meanwhile I thought more about the requirements, and kept only the most important two:
- - current version of the files must be available like a normal folder. No tools, or databases, or installations required to read them. Just mounting (or mapping) the NAS.
- - it must be able to restore any file from any time including the deleted or moved ones (like a "write only" incremental backup, I almost never delete and only rarely edit small source files, or rarely reorganize/move around the same folders). This way I can save to NAS the current version without checking I didn't accidentaly deleted something since the last save to NAS.