BTRFS RAID 1 works just fine with heterogeneous disks with no extra configuration required; I would not have been able to provide examples from experience other

BTRFS RAID 1 works just fine with heterogeneous disks with no extra configuration required; I would not have been able to provide examples from experience otherwise. When writing new data, it allocates two blocks on two separate devices, preferring to allocate space on whatever devices have the most free space. This may not be optimal from a performance perspective, but it does mean there's minimal wasted capacity in most configurations. (The RAID1c3 and RAID1c4 modes work the same, but with three or four copies of each block, all on separate devices.) Were you assuming that BTRFS RAID 1 meant every block of data gets mirrored across every device? I've seen that assumption before, from people who don't realize there are two ways to generalize RAID1 to more than two devices.