Windows 2000 Performance Guide

How the Windows 2000 File Cache Works

The Windows 2000 file cache works by converting (most) normal file I/O requests into requests for virtual memory mapped files. The Cache Manager interfaces to applications in several different ways. The standard interface is the Copy interface. Because it is entirely transparent to applications, the Copy interface is used by most applications. As the name implies, the Copy interface copies file data from a buffer inside the file cache to an application data file buffer on a read, and copies data in the opposite direction on a write.

Two other standard interfaces to the Windows 2000 file cache use memory more efficiently than the Copy interface: the Mapping interface and the MDL interface. Applications that want to take advantage of these Cache Manager interfaces must contain significant amounts of Windows 2000-specific code. The Windows 2000 file server service, Redirector, NTFS, and IIS use these more efficient interfaces.

The Copy Interface

Figure 7-4 diagrams in simple terms how the Copy interface functions for read hit requests. An application file read request calls the appropriate filesystem driver in Windows 2000, where the request is immediately routed to the Cache Manager. The Cache Manager maps each open file into the virtual memory reserved for the cache. This mapping is performed on 256 KB sections of a file at a time. Responding to the read request, the Cache Manager locates the block of data specified and copies it into an application-provided ...