Microsoft’s Web Capacity Analysis Tool

Microsoft’s Web Capacity Analysis Tool (WCAT) lets network administrators and Web masters optimize Internet or intranet servers by revealing how client requests for HTML and other content affect server performance. WCAT works with Windows 2000 (Win2K) or Windows NT servers running Microsoft Internet Information Server (IIS). You can get version 4.13 of WCAT from the Microsoft Windows 2000 Resource Kit, or you can download version 4.32 directly from Microsoft.

WCAT is a valuable tool for determining optimum network configuration and for aiding in capacity planning for your Web servers. The tool gives you dozens of prepared tests for evaluating server responses to client requests in various configurations. You can test several useful areas, including Secure Socket Layer (SSL) performance, support for cookies, and Active Server Pages (ASP) response.

You install the tool using a wizard that prompts you for the standard preferences, including whether you want a custom or a typical installation and where you want to install the software. If you choose to perform a custom installation, you can select from several options, as Screen 1 shows.

WCAT has four major components: server, client, controller, and network. Let’s take a look at each.

WCAT Server
The WCAT server typically consists of a Windows 2000 Server (Win2K Server) running IIS, but you can also use NT Server. The server uses a set of files specifically prepared to simulate a typical client accessing resources on a Web server. Each set of content files is associated with a particular WCAT test. You put the server through different levels of prepared tests to see how it might behave when clients request certain types of Web content. You can run these tests on most Web servers, but the WCAT documentation addresses some limitations (e.g., the tests won’t run on UNIX Web servers).

WCAT server requires that you have a Web server running TCP/IP with at least 220MB of available disk space. You can use Win2K Server, Windows 2000 Advanced Server (Win2K AS), Windows 2000 Datacenter Server (Datacenter), or NT Server 4.0. As for memory, you know the rule—the more the merrier. A physical RAM deficiency can compromise your tests. You must have enough to easily hold all static pages you’re testing.

WCAT Client
The client is a machine running the WCAT client application, which runs in a single multithreaded process. The individual threads represent a virtual client, so each client machine can simulate several clients. In fact, WCAT supports up to 200 virtual clients per computer.

A WCAT client requires Win2K Pro, Win2K Server, Win2K AS, Datacenter, NT Server 4.0, or Windows NT Workstation 4.0. The client computer must be running TCP/IP with at least 1MB of available disk space and a minimum of 8MB of RAM. Ideally, you should have at least 128MB of RAM to run Win2K Pro.

WCAT Controller
The WCAT controller application initiates the test and then monitors the results using three standard input files: a configuration file (.cfg), a script file (.scr), and a distribution file (.dst). An optional fourth file, the performance counter file (.pfc), specifies software performance counters for monitoring during testing. WCAT collects test activity statistics in two output files: the log file (.log) and the performance results file (.prf).

Like the WCAT client, the controller requires Win2K Pro, Win2K Server, Win2K AS, Datacenter, NT Server 4.0, or NT Workstation 4.0. A WCAT controller computer must be running TCP/IP with at least 10MB of available disk space and a minimum of 16MB of RAM (although I recommend at least 128MB of RAM).

WCAT Network
The link you establish between the client and the server during a WCAT test is the WCAT network. The client and the controller communicate using Windows Sockets. Microsoft recommends a TCP/IP network with a network bandwidth of at least 100Mbps to run WCAT tests.

WCAT Tests
With WCAT, you can either design your own custom tests to test a particular network configuration or simulate a workload by using one of the 40 prepared tests that come with the software. You can choose from among four basic types of WCAT tests: Basic, ASP, HTTP Keep-Alive, and SSL (see WCAT documentation for more about these tests). To run the tests, you need to go through a series of steps:

1. Prepare the controller input files.
2. Start WCAT Clients. From the \webclient folder, type wcclient.
3. Start WCAT Controller. From the \wcat\control folder, type wcctl.exe.
4. Start IIS.
5. Go through a warm up, experimental, cool-down, and a reporting period.
6. Prepare the controller output files.

The 60-page WCAT Guide, a Microsoft Word document you get when you download the software, explains in detail all the options, counters, switches, and other technical details. You can also refer to the online documentation at http://msdn.microsoft.com/workshop/server/toolbox/wcat.asp