ASP.NET MVC large number of file uploads dropped - asp.net

Question

We are hosting ASP.NET MVC app on Windows 2008 with IIS 7.5, 3 cores CPU(all usage ~60%) and 2GB of RAM. The w3wp.exe for the web app show ~700,000K of memory usage in task manager. Physical memory information is Total 2043, Cached ~600, Available ~611, Free ~20.
The web app accept large number of file uploads per minute. About ~20 files per minute. The file size range vary from 100kb to 10mb. We have noticed that many file uploads are dropped. While looking at HTTP request information we find that Content-Length and TotalBytes values are different.
The maxRequestLength is set to 81920 and executionTimeout 1200
<httpRuntime targetFramework="4.5" maxRequestLength="81920" executionTimeout="1200" />
Queue Length for app pool is set to 5000
We do not get any error in event viewer, we use custom file binder like this
[HttpPost]
public ActionResult UploadFile(IEnumerable<HttpPostedFileBase> clientUpload, [OptionModelBinder]IOptionViewModel formData)
{
//...
}
and get error in ASP.NET like this
System.ArgumentNullException: Value cannot be null.
Parameter name: name
at System.Reflection.RuntimeAssembly.GetType(String name, Boolean throwOnError, Boolean ignoreCase)
at System.Reflection.Assembly.CreateInstance(String typeName, Boolean ignoreCase, BindingFlags bindingAttr, Binder binder, Object[] args, CultureInfo culture, Object[] activationAttributes)
at PC.Controllers.OptionModelBinder.BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext)
at System.Web.Mvc.ControllerActionInvoker.GetParameterValue(ControllerContext controllerContext, ParameterDescriptor parameterDescriptor)
at System.Web.Mvc.ControllerActionInvoker.GetParameterValues(ControllerContext controllerContext, ActionDescriptor actionDescriptor)
at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass25.<BeginInvokeAction>b__1e(AsyncCallback asyncCallback, Object asyncState)
at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult`1.Begin(AsyncCallback callback, Object state, Int32 timeout)
at System.Web.Mvc.Async.AsyncResultWrapper.Begin[TResult](AsyncCallback callback, Object state, BeginInvokeDelegate beginDelegate, EndInvokeDelegate`1 endDelegate, Object tag, Int32 timeout)
at System.Web.Mvc.Async.AsyncResultWrapper.Begin[TResult](AsyncCallback callback, Object state, BeginInvokeDelegate beginDelegate, EndInvokeDelegate`1 endDelegate, Object tag)
at System.Web.Mvc.Controller.<>c__DisplayClass1d.<BeginExecuteCore>b__17(AsyncCallback asyncCallback, Object asyncState)
at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult`1.Begin(AsyncCallback callback, Object state, Int32 timeout)
at System.Web.Mvc.Async.AsyncResultWrapper.Begin[TResult](AsyncCallback callback, Object state, BeginInvokeDelegate beginDelegate, EndInvokeDelegate`1 endDelegate, Object tag, Int32 timeout)
at System.Web.Mvc.Controller.BeginExecuteCore(AsyncCallback callback, Object state)
at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult`1.Begin(AsyncCallback callback, Object state, Int32 timeout)
at System.Web.Mvc.Async.AsyncResultWrapper.Begin[TResult](AsyncCallback callback, Object state, BeginInvokeDelegate beginDelegate, EndInvokeDelegate`1 endDelegate, Object tag, Int32 timeout)
at System.Web.Mvc.Async.AsyncResultWrapper.Begin(AsyncCallback callback, Object state, BeginInvokeDelegate beginDelegate, EndInvokeDelegate endDelegate, Object tag)
at System.Web.Mvc.Controller.BeginExecute(RequestContext requestContext, AsyncCallback callback, Object state)
at System.Web.Mvc.MvcHandler.<>c__DisplayClass8.<BeginProcessRequest>b__2(AsyncCallback asyncCallback, Object asyncState)
at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncResult`1.Begin(AsyncCallback callback, Object state, Int32 timeout)
at System.Web.Mvc.Async.AsyncResultWrapper.Begin[TResult](AsyncCallback callback, Object state, BeginInvokeDelegate beginDelegate, EndInvokeDelegate`1 endDelegate, Object tag, Int32 timeout)
at System.Web.Mvc.Async.AsyncResultWrapper.Begin(AsyncCallback callback, Object state, BeginInvokeDelegate beginDelegate, EndInvokeDelegate endDelegate, Object tag)
at System.Web.Mvc.MvcHandler.BeginProcessRequest(HttpContextBase httpContext, AsyncCallback callback, Object state)
at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute()
at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)
The custom binder receive request but with partial upload data because Content-Length and TotalBytes do not match.
Maybe someone has any idea where the problem could be and where to start looking?

Answer 1

You have set maxRequestLength="81920", i.e. 80 mb. You have already mentioned large request may span to 100 mb, also Content-Length and TotalBytes are different. Please check if only those requests are failing those exceed size limit. If so, please increase maxRequestLength.