The HDFS web user interface serves useful information through dfshealth.jsp and dfsnodelist.jsp.
The Herriot interface to the namenode and datanode (as implemented in NNClient and DNClient, respectively) would benefit from the addition of some way to channel this information. In the case of DNClient this can be an injected method that returns a DatanodeDescriptor relevant to the underlying datanode.
There seems to be no analagous NamenodeDescriptor. It may be useful to add this as a facade to a visitor that aggregates values across the filesystem datanodes. These values are (from dfshealth JSP):
Non DFS Used
Number of Under-Replicated Blocks
Attributes reflecting the web user interface header may also be useful such as When-Started, Version, When-Compiled, and Upgrade-Status.
A NamenodeDescriptor would essentially "push down" the code in dfshealth web UI behind a more general abstraction. If it is objectionable to make this class available in HDFS, perhaps this could be packaged in a Herriot specific way.