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Scaling IIS 6.0

Updated: August 22, 2005

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

Changes in the Internet Information Services (IIS) 6.0 architecture have led to dramatic improvements in how IIS scales. During preliminary testing, IIS 6.0 scaled better than earlier versions of IIS. Those preliminary results showed that on a default installation, while running in worker process isolation mode, IIS 6.0 was capable of the following:

  • Hosting as many as 20,000 static-content sites.

  • Hosting as many as 2,000 application pools.

  • Processing 25,000 requests per second for a 15-KB cached static file with Hypertext Transfer Protocol (HTTP) Keep-Alives enabled.

  • Running hundreds — or potentially thousands — of simultaneous worker processes.

Performance and scalability results vary depending on hardware and software configurations. Microsoft does not make any warranties or guarantees about these preliminary results.

Additionally, processing throughput has greatly improved for installations with up to eight processors. Default thread pool, queue, and cache settings have all been tuned to increase throughput. Startup and shutdown times are faster than earlier versions. Simply put, your IIS Web server installation should scale better on a default installation of IIS 6.0 than on any earlier version of IIS. However, there are many variables in a Web server installation that can affect how IIS 6.0 scales. Scalability is dependent on the least scalable part in your server installation. Factors such as network latency, slow back-end processing, a shortage of RAM on your servers, or poorly designed and untested applications can all undermine how IIS 6.0 scales. If one part does not scale, the whole installation suffers.

This section provides a brief overview of the many changes and features that help IIS scale, and also describes some of the changes and features in the Microsoft® Windows® Server 2003, Standard Edition; Windows® Server 2003, Enterprise Edition; Windows® Server 2003, Web Edition; and Windows® Server 2003, Datacenter Edition operating systems that can increase the scalability of your server installation. Be aware that scaling an application server is a process much like tuning the performance of your server. Performance and scalability are intricately linked, and both goals require long-term planning, testing, and monitoring. For more information about performance monitoring and tuning, see Optimizing IIS 6.0 Performance.

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