title: Hadoop Metadata Types
body: <p>I'm researching Hadoop's metadata capabilities before our implementation of Hadoop. The term Hadoop Metadata seems to have multiple meanings.  I'll list three understandings that I have about the term.  But I'm looking to answer the question, "What metadata does Hadoop have for the data that is in it?"</p>
  
  <ol>
  <li><strong>Name node metadata</strong> - What exists so that the name node knows where data blocks are, what file the data blocks are composed of...  Basically stuff so Hadoop knows what data is where. (Does not seem like this is all that valuable as a metadata consumer although necessary.)</li>
  <li><strong>File metadata</strong> - From the file system shell.  Where I can get
  permissions number_of_replicas userid groupid filesize modification_date modification_time filename</li>
  <li><strong>HCatalog</strong> - (Incomplete understanding) Stores the schemas, or tables, information that was made by users via things like Hive and Pig.  Then I have schema-like metadata similar, howbeit limited, to say database metadata.</li>
  </ol>
  
  <p>So metadata in Hadoop seems a little fragmented to me.  I don't think I care what blocks are where for name node metadata.  But is there enough metadata somewhere in Hadoop to answer question like:
  What data is in Hadoop?
  What uses what data?
  When did the data get in Hadoop?</p>
  
  <p>To summarize my question: What useful metadata information does Hadoop have for metadata consuming purposes?</p>
  
  <p>Thanks.</p>