Now that some of the most standard hardware configurations have been presented and discussed, the next question that needs to be answered is how many users can a SharePoint 2003 server support. To answer this question, the type of use the server or server farm will get needs to be better defined. The Windows SharePoint Services 2.0 Administrator's Guide provides a definition of different levels of user activity and also provides information on the number of users who can be supported by different web servers and database server combinations. Per the Windows SharePoint Services 2.0 Administrator's Guide, a general rule of thumb can be used:
The user model for Windows SharePoint Services has two variables:
With these assumptions, Table 4.4 lists the number of users who can theoretically be supported by different server configurations. It is important to note that the data provided was generated by using automated load-generation tools, not actual users.
Figure 4.2 shows a graph of the transactions per second as they relate to the number of web servers and database servers. Information was not provided in the Windows SharePoint Services 2.0 Administration Guide for the number of transactions per second for the eight web servers by two database-servers configurations. Figure 4.2. Graph of transactions per second compared to server configuration.From Figure 4.2, it is clear that adding more than four web servers does not produce significant improvement. Adding a second database server dramatically improves the number of read transactions. Data was not provided for the results of a mixed read and write test of two databases. The server hardware configuration used to come up with this data is
A simplistic interpretation of this data suggests that a single system running Windows SharePoint Services with two slower processors and 1GB of memory can handle 10,200 extremely heavy users to 61,200 typical users performing read and write transactions. These numbers should be taken with a grain of salt, and testing should be performed on the specific SharePoint 2003 configuration in the organization's lab environment to determine whether the level of performance is acceptable to the user community. The automated tools used in this test probably didn't complain, whereas the user community certainly will. From a business standpoint, it makes sense to invest in more than a single server to support tens of thousands of users because if the single server crashes, there will be an overwhelming number of distressed users. Note also that other variables will affect the performance of the SharePoint 2003 server or server farm including other traffic on the network, virus protection software, security software and encryption technologies in use, and type of load balancing solution in use. Other Considerations in SharePoint Farm SizingAn alternative way of looking at server sizing takes into account the impact of failures on the organization. For example, an organization of 10,000 users may need only one Windows SharePoint Services server if usage is limited to 100 employees, and the impact to these users is minimal if the server goes down. For example, they may be able to survive without access to their sites for one or two days while a new machine is brought online and their sites are restored from tape. On the other hand, an organization with only 50 employees who use SharePoint Portal Server 2003 extensively not only for internal uses but also to collaborate with external clients and partners may suffer dire consequences if SharePoint is not available for more than a few minutes. Business could suffer, deadlines could be missed, and there could be financial consequences, or the reputation of the company could be hurt. In this case, a medium or even large server farm could be justified. Due to the number of variables involved, most clients approach the server farm design challenge from the business angle and use a strategy of "growth as needed," which justifies adding additional servers based on the levels of use and business impact of the SharePoint server farm. TIP A number of testing tools are on the market, including Mercury LoadRunner or Microsoft's Application Center Test (ACT) tool, which can be used during the prototype testing phase or to periodically test the performance of the SharePoint environment. These tools are designed to use minimal hardware resources to emulate hundreds or thousands of concurrent users to put applications through the rigors of real-life user loads. Microsoft's ACT tool is specifically designed to stress test web servers and analyze performance and scalability problems with web applications, including Active Server Pages (ASP) and the components they use. Application Center Test supports several different authentication schemes and the SSL protocol, making it ideal for testing personalized and secure sites. Capacity and Scaling Limits for Windows SharePoint ServicesInformation provided in the Windows SharePoint Services 2.0 Administrator's Guide highlights additional capacity and scaling limits for Windows SharePoint Services, as listed in Table 4.5.
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