What causes d:\ drive to be unavailable in web app on Azure?

Once in a blue moon, we get an exception from our Azure web app when initializing the cache.

The error message states Failed to start monitoring changes to 'D:\home\site'. A redeploy resolved the issue. We are using MvcDonutCaching, but I do not know if that is relevant.

Has anyone had a similar problem, and perhaps a suggestion to how we can resolve this?

System.Web.HttpException (0x80070035): Failed to start monitoring changes to 'D:\home\site'. at System.Web.FileChangesMonitor.FindDirectoryMonitor(String dir, Boolean addIfNotFound, Boolean throwOnError) at System.Web.FileChangesMonitor.StartMonitoringPath(String alias, FileChangeEventHandler callback, FileAttributesData& fad) at System.Web.Caching.CacheDependency.Init(Boolean isPublic, String[] filenamesArg, String[] cachekeysArg, CacheDependency dependency, DateTime utcStart) at System.Web.Caching.CacheDependency..ctor(String filename, DateTime start) at System.Web.Hosting.MapPathBasedVirtualPathProvider.CacheLookupOrInsert(String virtualPath, Boolean isFile) at System.Collections.Concurrent.ConcurrentDictionary2.GetOrAdd(TKey key, Func2 valueFactory) at System.Web.Mvc.BuildManagerViewEngine.FileExists(ControllerContext controllerContext, String virtualPath) at System.Web.WebPages.DefaultDisplayMode.GetDisplayInfo(HttpContextBase httpContext, String virtualPath, Func2 virtualPathExists) at System.Web.WebPages.DisplayModeProvider.GetDisplayInfoForVirtualPath(String virtualPath, HttpContextBase httpContext, Func2 virtualPathExists, IDisplayMode currentDisplayMode, Boolean requireConsistentDisplayMode) at System.Web.Mvc.VirtualPathProviderViewEngine.GetPathFromGeneralName(ControllerContext controllerContext, List1 locations, String name, String controllerName, String areaName, String cacheKey, String[]& searchedLocations) at System.Web.Mvc.VirtualPathProviderViewEngine.FindView(ControllerContext controllerContext, String viewName, String masterName, Boolean useCache) at System.Web.Mvc.ViewEngineCollection.<>c__DisplayClass6.<FindView>b__5(IViewEngine e) at System.Web.Mvc.ViewEngineCollection.Find(Func2 lookup, Boolean trackSearchedPaths) at System.Web.Mvc.ViewEngineCollection.FindView(ControllerContext controllerContext, String viewName, String masterName) at System.Web.Mvc.ViewResult.FindView(ControllerContext context) at System.Web.Mvc.ViewResultBase.ExecuteResult(ControllerContext context) at System.Web.Mvc.Async.AsyncControllerActionInvoker.<>c__DisplayClass21.b__1e(IAsyncResult asyncResult) at System.Web.Mvc.Async.AsyncControllerActionInvoker.EndInvokeAction(IAsyncResult asyncResult) at System.Web.Mvc.Controller.b__1d(IAsyncResult asyncResult, ExecuteCoreState innerState) at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncVoid1.CallEndDelegate(IAsyncResult asyncResult) at System.Web.Mvc.Controller.EndExecuteCore(IAsyncResult asyncResult) at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncVoid1.CallEndDelegate(IAsyncResult asyncResult) at System.Web.Mvc.Controller.EndExecute(IAsyncResult asyncResult) at System.Web.Mvc.MvcHandler.b__5(IAsyncResult asyncResult, ProcessRequestState innerState) at System.Web.Mvc.Async.AsyncResultWrapper.WrappedAsyncVoid`1.CallEndDelegate(IAsyncResult asyncResult) at System.Web.Mvc.MvcHandler.EndProcessRequest(IAsyncResult asyncResult) at System.Web.HttpApplication.CallHandlerExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() at System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously)

It's a temporary storage drive, so it shouldn't be used to store anything that needs to always be there. Perhaps, MvcDonutCaching needs to account for the temporary unavailability of the D drive? If so, please contact the dev team to check with them.

In the meantime, here are some useful articles:

Where is my data from disk D:

• http://vunvulearadu.blogspot.com/2013/02/windows-azure-virtual-machine-where-is.html

Change the Temporary Drive in a Azure VM and Use D: for Persistent Data Disks

• http://clemmblog.azurewebsites.net/change-temporary-drive-azure-vm-use-d-persistent-data-disks/

Hope that helps!