title: How can MongoDB dataSize be larger than storageSize?
body: <p>As far as I understand, the storage size for MongoDB should always be larger than data size. However, after upgrading to Mongo 3.0 and using WiredTiger, I start seeing that the data size is larger than the storage size.</p>
  
  <p>Here's from one of the databases:</p>
  
  <pre><code>{ 
      "db" : "Results", 
      "collections" : NumberInt(1), 
      "objects" : NumberInt(251816), 
      "avgObjSize" : 804.4109548241573, 
      "dataSize" : NumberInt(202563549), 
      "storageSize" : NumberInt(53755904), 
      "numExtents" : NumberInt(0), 
      "indexes" : NumberInt(5), 
      "indexSize" : NumberInt(41013248), 
      "ok" : NumberInt(1)
  }
  </code></pre>
  
  <p>Note that 202563549 > 53755904 by far margin. I am confused how this can be. Is the way to read <code>db.stats()</code> different now in Mongo 3.0?</p>