Capacity management is an ongoing process, because no implementation remains static in terms of content and usage. You need to plan for growth and change, so that your SharePoint-based environment can continue to deliver an effective business solution.
But the question is, Where to start? So to help you I have collected all the required links which provide information about the general concepts behind capacity management, as well as links to additional documentation and resources.
A site containing all available SharePoint Server 2010 capacity management documentation is available at http://technet.microsoft.com/en-us/library/cc262971(Office.14).aspx
Once you have a good understanding of the concepts, you can read about the limits and boundaries of SharePoint Server 2010 at SharePoint Server 2010 Limits and Boundaries
When you are ready to identify a starting point topology for your SharePoint-based environment, you can look through the library of available technical case studies to find the one that most closely matches your requirements Performance and capacity technical case studies
Capacity management white papers are available for many specific SharePoint services and features. Currently there are limited number of such white papers available, but more will be added as they become available. To download these white papers, visit http://technet.microsoft.com/en-us/library/ff608068(office.14).aspx
Read the documents for information about database sizing and performance at Storage and SQL Server capacity planning and configuration
Read the documents for information about remote BLOB storage (RBS) at Plan for remote BLOB storage (RBS)
Read the documents for information about health monitoring and troubleshooting using the health monitoring tools built into the Central Administration interface at Health monitoring & Solving problems and troubleshooting
The documents address general performance tuning guidelines and a variety of specific performance and capacity subjects. The list of available documents will grow as new content is developed Use search administration reports (SharePoint Server 2010)
For more information about virtualizing SharePoint-based servers, see Virtualization planning
Happy Capacity Planning !!!