Getting Started with SQL Server 2008 R2 - Microsoft SQL Server 2008 R2 Administration - page 29

For Data Warehouse, SQL Server Analysis Services (SSAS) supports OLAP (online analytical
processing) and data mining functionalities. This allows a database administrator to design
and create multidimensional structures that contain data aggregated from other data sources,
such as relational databases.
Analysis Services may be needed if the organization needs to rapidly access reports with
varying degrees of granularity (for example, yearly totals, monthly totals, quarterly totals,
and individual transactions) and requires that the yearly totals appear just as quickly as
the daily totals.
An online transaction processing (OLTP) system would have to add up these values, while an
SSAS system, in many cases, will already have the answers pre-calculated.
SQL Server Reporting Services (SSRS) delivers enterprise reporting functionality for creating
reports that gather content from a variety of data sources, publishing the reports in various
formats, and centrally managing their security and subscriptions. Reports can be delivered
on a scheduled basis to users, accessed through a web interface from SharePoint, or from
custom applications including Windows Forms applications that call through web services.
Reporting Services can be used to generate reports on OLTP databases, SSAS cubes, data
warehouses, data marts, or third-party data sources such as flat files, Oracle databases, or
web services.
How it works...
There are potential reasons why a database might not be located within an existing instance:
F Regulatory requirements: Corporate policies or government regulations may require
separate storage for certain types of data or for certain parts of the organization.
F Memory isolation: There may be a database application with a memory leak. It's
therefore desirable to place it in its own instance and cap the memory available to
this instance to protect other databases on the server from being affected.
F Fault tolerance: Clustering is on the instance level; thus, it will be necessary to place
a database in an instance with similar fault-tolerance requirements.
F Authentication: Authentication is set at the instance level to be either an SQL Server
authentication or a Windows authentication. The new database's authentication
requirements need to be compatible with the instance's authentication setting.
F Security concerns: Total database encryption can be used to add security to a
database. The service master key is for all databases in an instance. To minimize
exposure, if a key is compromised, it may be desirable to place the database in a
separate instance.
F Support requirements: The vendor or developer may require that the database runs
in a separate instance.