Btrfs

btrfs send /mnt/btr_backup/data.20150101 | btrfs receive /mnt/btr_pool/
btrfs subvolume snapshot /mnt/btr_pool/data.20150101 /mnt/btr_pool/data
btrfs subvolume delete /mnt/btr_pool/data.20150101

btrfs scrub start /

Find files with csum error

find /mount-point -type f -exec cp {} /dev/null \;

btrfs fi show
btrfs device add /dev/xxx /
btrfs balance start -dconvert=raid1 -mconvert=raid1 /

echo 1 | sudo tee /sys/block/sdb/device/delete
btrfs filesystem show /mountpoint
btrfs replace start -B <devid> /dev/new-disk /mountpoint
btrfs replace status
iostat -d 1 -m <target-dev>

http://www.moocowproductions.org/2014/12/04/fully-online-raid1-to-raid10-migration-using-btrfs/