=====BTRFS=====
===Never Use Parity Raid, EVER.===

===Make a subvolume ro/rw===

  btrfs property set -ts /path/to/snapshot ro (true|false)

===Backups===
https://btrfs.wiki.kernel.org/index.php/Incremental_Backup

  btrfs subvolume snapshot -r /mnt/snapshots/@rootfs /mnt/snapshots/$(hostname)-$(date +%Y-%m-%d)

# WRONG: This pushes backups to the backup server. We must pull from the host
# to the backup server!
  btrfs send -p /home/BACKUP-date /home/BACKUP | \
    ssh root@backups.narf.rocks \
    btrfs receive /backup/hostname.narf.rocks-date --

# UNTESTED
  btrfs receive /backup/$hostname-$date < \
    ssh root@$hostname \
    btrfs-send -p /backup/$hostname-$last_backup_date /backup/$hostname-$date