 <p>Look at signature:</p> <pre><code> IEnumerable&lt;SafeModeResult&gt; InsertBatch( Type nominalType, IEnumerable&lt;Object&gt; documents, SafeMode safeMode </code></pre> <p><a href="http://api.mongodb.org/csharp/1.1/html/cac72c74-ae6d-9b2e-a503-303a40104143.htm" rel="nofollow">SafeMode</a> can cause postpone you real batch write. Play with <code>FSyncTrue</code> (can be very slow) or <code>True</code>.</p>