Use fsck, it's a tool of choice to manage HDFS. "Orphans" are corrupted files (with missing blocks) in HDFS lingo. You can use "-move" or "-delete" options to move corrupted files to /lost+found or to delete them. fsck will also tell you about under-replicated blocks (having at least 1 replica but less than configured replication factor) but HDFS will repair them little by little by creating missing replicas.