title: Does the upgrade to MongoDB 3.0 Wired Tiger still report data size correctly to MMS?
body: <p>I'm curious as to why my MMS is suddenly showing a rapid data growth since I've upgraded to Mongo 3.0 (Wired Tiger storage engine).  The slope of the new growth the past couple weeks directly correlates with the upgrade.  There are only a couple collections in this database that have over 500 documents...though these are both huge collections, the document structure has remained the same before an after the upgrade.  Also running aggregations on these collections indicate that the number of inserts has not changed on average before/after the upgrade.  This leads me to question whether the data size is being calculated differently with the new WiredTiger engine or something of that matter.  Does anyone have any information on this?  Here is an image of my MMS data.</p>
  
  <p><img src="https://i.stack.imgur.com/V9G5S.jpg" alt="enter image description here"></p>
  
  <p>A couple things, there are 2 jumps in size...these are times when I migrated a collection over from another database to mongo.  Still after both of these the growth rate remained consistent and only increased after the upgrade.  The data size decreased at the upgrade (consistent with they hypothesis that Wired Tiger has compression) but has been growing so quickly that it has almost reached it's original size.  Even the Storage Size has started growing much faster than it originally did, though this image doesn't do it justice.</p>