Cube Storage MOLAP vs ROLAP vs HOLAP

Cube data includes meta-data, detail-data, and aggregate data. Meta-data always stored on the OLAP, the other two stored depending on the storage mode.

MOLAP (Multidimensional OLAP)

MOLAP is default and most frequently used storage, it has maximum query performance because after each cube processing, detail-data and meta-data would be stored locally on the OLAP in a compressed and optimized multidimensional format

Pros of MOLAP:

• All calculations are pre-generated when the cube is processed.
• Don't need permanent connection to the underlying relational database.
• Has maximum query performance.

Cons of MOLAP:

• Need frequent processing to pull refreshed data.
• Latency: Any changes in the relational database will not reflected after the processing.
• If data volume is huge, cube processing needs times. You can use incremental processing to avoid this.
• Needs additional storage to store relational data.

ROLAP (Relational OLAP)

ROLAP didn't pull data from relational database. It stored detail-data and aggregate data in a format of additional database objects such as indexed views within the relational database source rather than OLAP. 

Pros of ROLAP: 

• Ability to view the data in almost real time.
• Has less storage requirement as no other copy of source data required. 
• Can handle huge data source with no size limitation. This is because the detail-data is stored in the underling relational database. 

Cons of ROLAP: 

• Query response is quite slower as everything you want is through accessing relational database source rather than OLAP.
• Permanent connection is needed while viewing cube data.

HOLAP (Hybrid OLAP)

HOLAP is hybrid of MOLAP and ROLAP in which to include high query response time and performance from MOLAP while maintaining high data capacity from ROLAP.  In HOLAP, the detailed data stored at underling database source while the aggregate data stored at OLAP server.
Thus, querying aggregate data is same as MOLAP with high performance. For detail data query, HOLAP will go inside the source database with slower performance.

Pros of HOLAP: 

• Balance of the disk requirement and query performance.
• Has less storage requirement as no other copy of source data required. 
• Can handle huge data source with no size limitation. This is because the detail-data is stored in the underling relational database. 
• Quick query response for aggregate data.

Cons of HOLAP: 

• Query response is quite slower for detailed data.

Summary

Storage Mode	Detail Data	Summary/ Aggregations	Storage space requirement	Query Response Time	Processing Time	Latency
MOLAP	OLAP	OLAP	Medium	Fast	Fast	High
HOLAP	Relational DB Source	OLAP	Small	Medium	Fast	Medium
ROLAP	Relational DB Source	Relational DB Source	Large	Slow	Slow	Low

Source:

http://www.sql-server-performance.com/2013/ssas-storage-modes/