Presently, a peer can be detached only if no volumes in cluster exist with bricks on that peer. If a peer contains bricks that belong to a volume in the cluster, detach fails. A 'force' option is useful in such cases. Suggested by Vijay.
CHANGE: http://review.gluster.com/429 (Adds add a 'force' option to 'peer detach' to forcefully detach a peer from a) merged in master by Vijay Bellur (vijay)