storage modes in ssas

SQL server analysis service uses three different storage modes for storing data into Cube.

• MOLAP – Multi-dimensional online analytical processing
• ROLAP – Relational online analytical processing
• HOLAP – Hybrid online analytical processing

What is MOLAP?
In MOLAP mode, Data will store in multi-dimensional cube. The storage is not relational database but its proprietary format.

Advantage:

• Excellent performance
• Can perform complex calculation – All calculation is pre-generated when cube is created.

Disadvantage:

• Limited data it can handle – All calculation are performed when cube is built. It is not possible to store large amount of data into cube itself.

What is ROLAP?
In this mode, Data is stored in relational database instead of cube itself.

Advantages:

• Can handle large amount of data
• Can leverage functionalities inherent in the relational database

Disadvantages:

• Performance can be slow
• Limited by SQL functionalities

What is HOLAP?
HOLAP attempts to combine ROLAP and MOLAP. When Data is very large then SSAS use ROLAP and when data is very limited then SSAS use MOLAP.