sqlite on NFS volumes can be very problematic (i.e. operations that normally take seconds can take hours). When createrepo_c generates sqlite metadata, please use a temp directory on local disk and then move the end result to the repodata directory. This would save from having to use --output-dir as a workaround.
Good point! I've just added new option --local-sqlite [1]. This option is available since version 1.7.2 which was just built in rawhide [2]. [1] https://github.com/Tojaj/createrepo_c/commit/5130231cea086c986593f572b94f88b35c4ce607 [2] http://koji.fedoraproject.org/koji/taskinfo?taskID=8054826