Pretty much all commands print out the usage message when no device is specified:
[root@host ~]# btrfs scrub start btrfs scrub start: too few arguments usage: btrfs scrub start [-BdqrRf] [-c ioprio_class -n ioprio_classdata] <path>|<device> ... However, balance doesn't [root@host ~]# btrfs balance start ERROR: can't access 'start': No such file or directory -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
