Increasing bigcouch disk usage

root@ant:/opt/bigcouch/var/lib# du -sch * .*
3.3G	dbs.couch
224K	nodes.couch
8.0K	_replicator.couch
4.5G	shards
300K	_users.couch
…
13G	total

(from redmine: created on 2015-02-11, closed on 2016-05-26, relates #6741 (closed), relates #4798 (closed), relates #4761 (closed))