Caching UNC-based Files

Applies To: Windows Server 2003, Windows Server 2003 with SP1

When you can create UNC-based virtual directories, the IIS caches must treat each UNC path as a separate directory structure, and therefore ASP and static file caches must monitor each directory individually. In a centralized-content architecture with many different UNC shares, this has the potential to exhaust system resources.

The Web server and the file server are connected with a Server Message Block (SMB) connection. Only one SMB connection is created between a Web server and a file server; however, within that SMB connection, there are a finite number of work items. Work items can be consumed in a variety of ways and for varying amounts of time. For example, performing an operation — such as a CreateFile or GetFileAttributes command — on a file consumes an I/O work item for a short amount of time, but asking for a change notification on a directory structure consumes a work item for as long as the connection is intact. Each change-notification instance uses a work item until the connection is lost, and each request from a Web server to the file server uses a work item only temporarily. However, the scalability impact of the SMB connection is reduced by using last-modified caching.

IIS 6.0 has two methods for caching static and ASP files, called last-modified caching and change-notification caching. For information about configuring change-notification tracking or the time to live (TTL) for static and ASP files, see Configuring Last-Modified Caching and Configuring ASP Change-Notification Caching.