Since you asked me, it was many years ago now (5+) - but it hurt. I lost a 16TB cluster to btrfs, the raid just failed for no apparent reason (this wasn't uncommon back then according to forums). And on ZFS it was a kernel bug where on boot, it would mount ZFS after waiting for root - so root never appeared. (This was due to ZFS running as a user-space driver on linux back when it wasn't yet in the kernel)