dd if=/dev/zero of=1gb_root bs=1G count=1
dd if=/dev/zero of=1gb_backup bs=1G count=1
losetup -f 1gb_root
losetup -f 1gb_backup
mkfs.btrfs -L TEST_ROOT /dev/loop0
mkfs.btrfs -L TEST_BACKUP /dev/loop1
mkdir mnt/TEST_ROOT
mount -o compress=lzo /dev/loop0 mnt/TEST_ROOT/
btrfs subvolume create root
btrfs subvolume list mnt/TEST_ROOT/
	ID 257 top level 5 path root
btrfs subvolume set-default 257 mnt/TEST_ROOT
umount mnt/TEST_ROOT
mount -o compress=lzo /dev/loop0 mnt/TEST_ROOT/
mkdir mnt/TEST_ROOT/root_volid0
mkdir mnt/TEST_ROOT/backup_volid0
mount -o subvolid=0,compress=lzo /dev/loop0 mnt/TEST_ROOT/root_volid0
mount -o compress=lzo /dev/loop1 mnt/TEST_ROOT/backup_volid0
btrfs subvolume create mnt/TEST_ROOT/backup_volid0/backup
btrfs subvolume list mnt/TEST_ROOT/backup_volid0/
	ID 257 top level 5 path backup
umount mnt/TEST_ROOT/backup_volid0
mount -o subvolid=0,compress=lzo /dev/loop1 mnt/TEST_ROOT/backup_volid0

mount | grep btrfs:

/dev/loop0 on /home/robert/ArchLinux/tests/btrfs/mnt/TEST_ROOT type btrfs (rw,relatime,compress=lzo,space_cache)
/dev/loop0 on /home/robert/ArchLinux/tests/btrfs/mnt/TEST_ROOT/root_volid0 type btrfs (rw,relatime,compress=lzo,space_cache)
/dev/loop1 on /home/robert/ArchLinux/tests/btrfs/mnt/TEST_ROOT/backup_volid0 type btrfs (rw,relatime,compress=lzo,space_cache)

btrfs subvolume snapshot -r mnt/TEST_ROOT/root_volid0/root/ mnt/TEST_ROOT/root_volid0/root_snap
btrfs send mnt/TEST_ROOT/root_volid0/root_snap > root_snap_send
btrfs receive -f root_snap_send mnt/TEST_ROOT/backup_volid0/
	ERROR: utimes  failed. Bad file descriptor
#root_snap in backup_volid0 is empty :/