An Overview of Capacity Planning

In order to realize the full potential of a site,you have to satisfy the demands of your users, which typically consist of quality of service, quality of content, and speedy access to the site's content and services. (The latter is, for most of your users, the key contributing factor to a positive user experience.) Capacity planning is the process of determining the most cost efficient method of increasing a Web site's performance and scalability, while at the same time predicting the point at which a resource will cause a bottleneck on the Web site.

The starting point for capacity planning is determining a site's capacity, which is determined by:

• The number of users it can handle before performance falls off
• The server's ability to handle increased load, either due to an increased number of users or increased content complexity
• The nature of the site's content, which is to say, the complexity of its applications

NOTE

---

Capacity is influenced indirectly by performance; a well-tuned site can increase capacity by making better use of existing resources and, in some cases, free up resources. At some point, regardless of how well tuned your site is, the site cannot handle more traffic without degrading performance. This is the point at which you either have to scale up by upgrading/replacing the existing servers or scale out by increasing the size of your cluster.

Ideally, you will have done some capacity planning that establishes acceptable performance benchmarks and resource usage limits, and you will have either scaled or have a plan in place to scale your system before performance degrades.

The key factors for successful capacity planning are:

• Understanding the nature of the site's content. Different types of content (for example, static HTML pages and ASP pages) have a different—and often dramatic—impact on system resources. Your capacity planning has to take into account how the existing content types affect capacity, as well as how a change in the content mix could affect resource usage.
• Understanding the site's users. You have to be able to understand site usage patterns in order to predict traffic growth and accommodate short-term usage spikes.

Once again, you have to gather baseline data before you can determine when and how to increase the capacity of your system.

We recommend that you use the "Capacity Planning" white paper (Microsoft TechNet) as a guide for your capacity planning activities. The Microsoft Internet Information Server Resource Kit (Microsoft Press, 1998) for IIS 4.0 and the Microsoft Information Services Resource Guide (Microsoft Press, 2000) for IIS 5.0 also provide useful information about capacity planning for Web sites.

White Paper: "Capacity Planning"

The "Capacity Planning" white paper, produced by Microsoft Enterprise Services, is available from the TechNet Web site at the following URL: http://www.microsoft.com/TechNet/ecommerce/capplan.asp.

"Capacity Planning" is a part of a series about applying Microsoft Enterprise Services frameworks to e-commerce solutions, and although it deals with capacity planning for sites running Windows 2000, IIS, Microsoft Site Server version 3.0, and Microsoft SQL Server version 7.0, it's methodology is not limited to these products or this particular business solution.

The following topics and subtopics are covered in the white paper:

• "Introduction to Capacity Planning"
  The introduction covers the why, when, and how of capacity planning and introduces the capacity planning equation:
  Number of supported users = Hardware capacity/load on hardware per user
• "Analyzing Your Site"
  "Dynamic Content Analysis"
  "Site Server 3.0 Commerce Edition"
  "Transaction Cost Analysis"
  "Predicting Site Traffic"
  "Analyzing a Typical User"
  "Acceptable Operation Parameters"
  "A Detailed Test Methodology"
  "User Cost Calculations" (for CPU, memory, disk, and network)
• "Deriving Site Capacity"
  In this section, you'll learn how to calculate hardware needs and how to plan site topology scalability—both vertically and horizontally.