Critical Description
We need to fsync the parent directory when flushing – creating new cfiles, new metadata superblock files, etc. We can use the Env::SyncDir() call added by Alex in http://gerrit.ent.cloudera.com:8080/#/c/2544/
For some general guidance on this see the post by Robert Love on Quora: http://www.quora.com/Linux/When-should-you-fsync-the-containing-directory-in-addition-to-the-file-itself