Looking at solrhome/data directory in my solrcloud cluster I have found a lot of old snapshot directories like these:
snapshot.20150506003702765
snapshot.20150506003702760
snapshot.20150507002849492
snapshot.20150507002849473
snapshot.20150507002849459
or even a month older. These directories keep really a lot of space, 2 or 3 times the whole index.
May I delete these directories? If yes, is there a best practice, should I restart solrcloud?
Those directories are created with the Solr replication handler and are safe to delete; they're not currently in use so no restart is required. Full documentation is available here.