Concerning the BTRFS fs:

I did use it as well many years ago (probably around 2012-2015) in a raid5-configuration after reading a lot of positive comments about this next-gen fs => after a few weeks my raid started falling apart (while performing normal operations!) as I got all kind of weird problems => my conclusion was that the raid was corrupt and it couldn't be fixed => no big problem as I did have a backup, but that definitely ruined my initial BTRFS-experience. During those times even if the fs was new and even if there were warnings about it (being new), everybody was very optimistic/positive about it but in my case that experiment has been a desaster.

That event held me back until today from trying to use it again. I admit that today it might be a lot better than in the past but as people have already been in the past positive about it (but then in my case it broke) it's difficult for me now to say "aha - now the general positive opinion is probably more realistic then in the past", due e.g. to that bug that can potentially still destroy a raid (the "write hole"-bug): personally I think that if BTRFS still makes that raid-functionality available while it has such a big bug while at the same time advertising it as a great feature of the fs, the "irrealistically positive"-behaviour is still present, therefore I still cannot trust it. Additionally that bug being open since forever makes me think that it's really hard to fix, which in turn makes me think that the foundation and/or code of BTRFS is bad (which is the reason why that bug cannot be fixed quickly) and that therefore potentially in the future some even more complicated bugs might show up.

Concerning alternatives:

I am writing and testing since a looong time a program which ends up creating a big database (using "Yandex Clickhouse" for the main DB) distributed on multiple hosts where each one uses multiple HDDs to save the data and that at the same time is able to fight against potential "bitrot" ( https://en.wikipedia.org/wiki/Data_degradation ) without having to resync the whole local storage each time that a byte on some HDD lost its value. Excluding BTRFS, the only other candidate that I found is ZFSoL that perform checksums on data (both XFS and NILFS2 do checksums but only on metadata).

Excluding BTRFS because of the reasons mentioned above, I was left only with ZFS.

I'm now using ZFSoL since a couple of months and so far everything went very well (a bit difficult to understand & deal with at the beginning, but extremely flexible) and performance is as well good (but to be fair that's easy in combination with the Clickhouse DB, as the DB itself writes data already in a CoW-way, therefore blocks of a table stored on ZFS are always very likely to be contiguous).

On one hand, technically, now I'm happy. On the other hand I do admit that the problems about licensing and the non-integration of ZFSoL in the kernel do have risks. Unluckily I just don't see any alternative.

I do donate monthly something to https://www.patreon.com/bcachefs but I don't have high hopes - not much happening and BCACHE (even if currently integrated in the kernel) hasn't been in my experience very good (https://github.com/akiradeveloper/dm-writeboost worked A LOT better, but I'm not using it anymore as I don't have a usecase for it anymore, and it was a risk as well as not yet included in the kernel) therefore BCACHEFS might end up being the same.

Bah :(