My main issue isn't actually a single thing that's wrong -- it's the completely and utterly haphazard way many of the features in btrfs have been "designed"[1]. Some of these problem they've had seem, to me at least, to be a fundamental lack of a coherent design. That does not bode well for stability, even 10(?) years after its first version.

bcachefs seems to have a much more coherent design.

[1] "Oh, yeah, I don't know how to handle this code path yet, let's stick a BUG_ON in there! I'm sure we'll figure something out later."

I think Chris Mason is open with that raid support is not really stable yet, right?

Status page says so: https://btrfs.wiki.kernel.org/index.php/Status

As far as I know they consider RAID0, 1, and 10 to be stable. Last time I used it rebuilds were substantially slower than ZFS or mdraid. Rebuild performance seems to one of a few issues that BTRFS has had trouble solving. RAID 5 and 6 were declared stable last year, only to have that retracted when some fatal flaw was discovered that would apparently cause data loss if you needed to rebuild.

It's mostly true but the issues as far as I know are:

- RAID 1 with more than 2 disks is not what you think it is: the data will be mirrored but only once, no matter how many disks you have (meaning if you have a mirror with 3 disks, you only have 2 copies of your data). Because in BTRFS lingo, RAID 1 means '2 copies of the data' https://btrfs.wiki.kernel.org/index.php/FAQ#What_are_the_dif... which is not what people expect from RAID 1 with more than 2 disks

- RAID 1 always needs 2 disks to be working, if not you can't mount the thing... Well you can, but only once... https://btrfs.wiki.kernel.org/index.php/Gotchas#raid1_volume...

- RAID 10 inherits these special RAID 1 cases as a result

Most of that stuff is described here: https://btrfs.wiki.kernel.org/index.php/Status

So as they say on the status page: "mostly ok"