Designing Storage Options and Aggregations

Designing Storage Options and Aggregations

Use the Storage Design Wizard to quickly and easily set storage options and design aggregations for a partition. The wizard operates on a single partition at a time so that you can select different options and designs for each partition. If you start the wizard by selecting a multiple-partition cube, the wizard prompts you to select a partition. You can also start the wizard by selecting a single-partition cube or a partition. The wizard takes you through steps to specify storage and aggregation options for a partition.

Select a storage option if no aggregations exist or if you choose to replace existing aggregations. Each option is briefly described in the following table.

Storage option	Description
MOLAP	Multidimensional OLAP (MOLAP) stores aggregations and a copy of the partition's source data in a multidimensional structure on an Analysis server computer.
ROLAP	Relational OLAP (ROLAP) stores aggregations in a relational structure and leaves the partition's source data in its existing relational structure.
HOLAP	Hybrid OLAP (HOLAP) stores aggregations in a multidimensional structure on an Analysis server computer and leaves the partition's source data in its existing relational structure.

Each storage option has advantages and disadvantages. For more information, see Partition Storage.

Aggregations are precalculated summaries of cube data that help enable Microsoft® SQL Server™ 2000 Analysis Services to provide rapid query responses. Select a method of controlling the number of aggregations the wizard will design, and then let the wizard design the aggregations.

The goal is to design the optimal number of aggregations. This number should not only provide satisfactory response time, but also prevent excessive partition size. A greater number of aggregations produces faster response time but it also requires more storage space. Moreover, as the wizard designs more and more aggregations, earlier aggregations produce considerably larger performance gains than later aggregations. You can control the number of aggregations the wizard designs by one of the following methods available in the wizard:

• Specify a storage space limit for the aggregations.
  
  
• Specify a performance gain limit.
  
  
• Stop the wizard manually when the displayed Performance vs. Size curve starts to level off at an acceptable performance gain.

For more information about aggregations, see Aggregations.

The final step of the wizard allows you to process or defer processing. Processing creates the aggregations you design with the wizard, while deferring processing saves the designed aggregations for future processing, thus allowing design activities to continue without having to process. Depending on the size of the partition, processing may take considerable time.

To start the Storage Design Wizard