There are three physical storage modes for the data in a cube: MOLAP, ROLAP, and HOLAP.

• MOLAP (Multidimensional OLAP) is the default and the fastest. It makes a copy of the base data from the source (normally a star schema) and stores that data in a binary format. Aggregations are stored in the same binary format. In my experience, I've used MOLAP about 99% of the time.
• ROLAP (Relational OLAP) keeps the base data in the source and stores any aggregations in relational tables created for that purpose. It is generally the slowest of the three methods. The benefit is that it supports real-time OLAP (MOLAP can fake it pretty well, but ROLAP does it for real.) In my experience, I've used ROLAP about 1% of the time.
• HOLAP (Hybrid OLAP) keep the base data in the source but stores aggregations in the MOLAP format. Performance is as fast as MOLAP at higher levels of detail but as slow as ROLAP at the lowest level of granularity. In my experience, I've never used HOLAP.

You set this at the partition level. Click on the Partitions tab (when editing a cube.) You can then set the storage mode.You can also set dimension storage to either MOLAP or ROLAP.

mauryakamal wrote Thanx Cutely.. My query.. 1. What is the Real time what does it mean(Please explain it ) - Real-time BI means that as each record comes into a transactional system, the new data is reflected in the data warehouse. Warehouses are normally updated on a regular schedule, such as nightly, so the data is out of date the next day. Usually that's fine, but some companies want the warehouse up to date in real time. 2. is it ROLAP created automatically relational tables to store any aggregations? - Yes. 3. In MOLAP storage will be get the always old data not updated one? - MOLAP is up to date when you do a process. As soon as the next record makes it into the system, the cube is out of date. This usually isn't a problem (nightly updates are pretty common) but you could reprocess every five minutes if you wanted. 4. when we will use the ROLAP instead of the MOLAP storage. - You'll use ROLAP if you need true real-time data in the cube. I've only ever used it once and it was a really strange situation. Thanx in advance..   kamal maurya

See my comments in the quote above.