This hasn't been my experience. When an md array has lost a disk, I have added a new one and the array has transparently resynched in the background. No inter

This hasn't been my experience. When an md array has lost a disk, I have added a new one and the array has transparently resynched in the background. No interruption in service or loss of data. When a Btrfs array has lost a disk, Btrfs oopsed the kernel, and stopped working. When I rebooted with the hardware problem resolved, it toasted both the outdated mirror and the up-to-date disk, causing irretrievable dataloss. Any attempt to boot the system led to Btrfs causing an immediate kernel panic. I had to put the disks into a system without Btrfs kernel support and use dd to zero out the Btrfs partitions before I could use them again. That was admittedly a few years back, but it's still a long way from production use in many respects, while ZFS has been in production use for years and is well documented, has good tools, and is very robust. After several years of Btrfs problems, I gave up on it and moved to ZFS, initially on Linux and then on FreeBSD due to it being better integrated.