The capacity of Microsoft Windows SharePoint Services version 3.0 is also limited by scalability — that is, how many objects can be created in a given scope (for example, number of documents per folder). The scale limits in Windows SharePoint Services are not hard limits enforced by the system; rather, they are practical limits imposed by reasonable performance. In other words, you can exceed these limits if you want to, but you may find the resulting performance to be unacceptable. See ScaleLimWSS3 for more details.

When you decide to implement a server farm, it is generally because you want to support a large-scale Web environment.

Achieving scalability depends on a number of factors, each of which must be regulated in its own way.

These factors include:

• The amount of processing power available for each Web site
  You can manage processing power by ensuring that you have appropriate load balancing up front, and a good balance between the number of front-end Web servers and Microsoft SQL Server back-end servers. A recommended minimum configuration for a server farm includes three front-end Web servers and two back-end database servers.
  
• The amount of disk space available for Web site content and data
  You can manage disk space issues by using quotas to limit Web site size, and by specifying maximum sizes for content databases.
  
• Protection from single-box failure
  Using multiple front-end Web servers to serve the same content gives you protection from failure on the front end. You can use the failover protection included with SQL Server 2005 to help protect your back-end servers.
  
• The number of sites stored in each content database
  You will get better results by limiting the size of each content database and simply adding more content databases when you add more sites. Smaller content databases make it easier to back up and restore or move sites.
  

  Note:
  Database performance may degrade if you add too many databases. Balance your needs for backup and restore performance against those for database performance.

Balancing the load for the front-end Web servers is also part of the scalability equation. Windows SharePoint Services supports two methods of load balancing:

• Software, such as Network Load Balancing (NLB) services in Windows Server 2003
  NLB runs on the front-end Web servers and uses the Transmission Control Protocol/Internet Protocol (TCP/IP) networking protocol to route requests. Because NLB (and other software load-balancing solutions) runs on the front-end Web servers, it uses the front-end Web system resources, thereby limiting the resources you can use for serving Web pages. However, the impact on system resources is not great, and a software solution can handle up to 32 front-end Web servers.
  
• Hardware, such as a router or switch box
  Load-balancing hardware uses your network to direct Web site traffic between your front-end Web servers. Load-balancing hardware is more expensive to set up than software, but does not use any of your front-end Web server resources to run. You can use Windows SharePoint Services with any load-balancing hardware.
  

There is a third method of load balancing: round-robin load balancing with Domain Name System (DNS). Round-robin DNS load balancing uses a lot of resources on the front-end Web servers, is slower than either load-balancing software or hardware, and is not recommended for use with Windows SharePoint Services.