You’ve probably heard the term scalability, but few people take the time to define it for themselves. In this book, scalability is the ability of a server to handle an additional load without significant performance degradation. When you add a second user, the server may slow a little, but not enough for anyone to notice. Adding three or more users also incurs a small, barely noticeable performance degradation. Even when a server is scalable, it eventually reaches a maximum load where it can’t handle even one more user. When every resource is used, albeit used as efficiently as possible, the server has reached a maximum load and can’t handle another user no matter how you might try to coax it. Many people feel that scalability is limitless. All scalability really does is make the server perform better across its load range — there isn’t any magic involved in the process. Of course, a scalable server can extend its load slightly because it uses resources more efficiently. Windows Server 2008 provides many levels of additional scalability over previous editions of Windows. The focus of this chapter is hardware, and you’ll find many scalability improvements in this area. You can categorize the improvements in three ways:
• Improved software support: Using drivers and support software that improves overall server performance also improves scalability. Every time Windows Server 2008 uses a resource more efficiently, the resource availability extends to users, processes, drivers, and other entities that need it. The new XML Paper Specification Driver (XPSDrv) is an example of improved software that provides a performance and scalability boost.
• Direct device participation: Many devices now include some level of intelligence. By leveraging that intelligence, Windows Server 2008 can offload part of the processing requirements to the device, which frees server resources for other uses. The new Web Services on Devices (WSD) functionality is an example of how Windows Server 2008 supports device participation.
• Direct client participation: Clients make many requests and then wait for the server to respond to them. While the client sits and idles, many of the processor cycles that it could use end up wasted. Providing ways for the client to participate in handling a particular request makes the server more scalable.
The amount of scalability that a server achieves often depends on the cooperation of these three elements. For example, the amount of processing burden that the server can offload to the client depends on the Page Description Language (PDL) that the print job uses and the content of the document itself. Some forms of PDL and content require a certain level of server participation. Printing a report that depends on content from a database using PostScript is far less likely to enhance scalability than a plain-text print job that relies solely on the content in Word.
The client also affects how scalable the server becomes. Microsoft’s technology appears to depend on communicating with a Vista client to achieve maximum scalability. Obviously, someone has to run tests, at some point, to demonstrate this reliance because Microsoft isn’t saying much (although its marketing literature often fails to mention Windows XP as a client). My own tests indicate that Windows Server 2008 prefers Vista as a client.
Windows Server 2008 also uses Remote Procedure Calls (RPCs) more efficiently. An RPC is a call from the client to the server for specific needs, such as the print spooler. By using RPC calls more efficiently and relying on fewer of them, Windows Server 2008 gets a scalability boost, especially in a medium to large company environment (where even small differences can mean a lot).
Source of Information : For Dummies Windows Server 2008
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