HDFS-744 adds support for true durable sync for DFSOutputStream.hsync().
This is useful for HBase (among others) and I created a matching patch in HBASE-5954.
I would like to port this back into Hadoop 2.0 and maybe even 1.0.
A 2.0 patch is already attached to HDFS-744. (The 1.0 patch would be quite different, but the underlying implementation would be the same)
If I understand correctly Hadoop 2.0 is not out of alpha, yet.