How to upload really big files on server in ASP.NET ?

Apart from setting httpRuntime maxMessageLength property in web.config file below

 <system.web>
  <httpRuntime maxMessageLength="409600"
    executionTimeoutInSeconds="300"/>
  </system.web>

We also need to set below settings in system.webServer so that it can upload up to 100 MB file

<system.webServer>
<security>
      <requestFiltering>
        <!-- in byte - 100 MB size below -->
        <requestLimits maxAllowedContentLength="104857600" />
      </requestFiltering>
    </security> 
</system.webServer>

To allow more than 100 MB, change the maxAllowedContentLength value.

Hope this helps.

Thanks