These filesystems are not really alternatives because mdraid supports features those filesystems do not. For example, parity raid is still broken in btrfs (so it effectively does not support it), and last I checked zfs can't grow a parity raid array while mdraid can.

I run btrfs on top of mdraid in RAID6 so I can incrementally grow it while still having copy-on-write, checksums, snapshots, etc.

I hope that one day btrfs fixes its parity raid or bcachefs will become stable enough to fully replace mdraid. In the meantime I'll continue using mdraid with a copy-on-write filesystem on top.

> zfs can't grow a parity raid array while mdraid can.

indeed out of date - that was merged a long time ago and shipped in a stable version earlier this year.

soon :)