Retention Warehouse 
Retention Warehouse is the third cornerstone of ILM from SAP, and it involves different tools and methods for implementing a standardized process for system decommissioning, which also allows you to continue to use the archived data for reporting purposes or audits even though the original system has been shut down. The retention warehouse processes are tightly integrated with the other two cornerstones of ILM from SAP.
Process
The basic process of the retention warehouse cornerstone is divided into two main phases: system decommissioning and auditing and reporting.
System decommissioning: in the phase you use classical and enhanced data archiving options to empty the system of its data, and then you store the data in an ILM-aware storage system. The phase ends with the shut-down of the system.
Auditing and reporting: this phase may occur years after the original system has already been shut down. It consists of selecting the needed data in the archive and preparing it for upload into BI infoproviders. In SAP NW BI you can then run queries on the data or use it in an audit. When you are done, the infoproviders can be deleted and the data continues to rest in the ILM-aware storage system until it can be destroyed.
The following graphic shows the basic steps involved in the two phases:
The Two Phases of the Retention Warehouse Process
More Information
For more information on the retention warehouse cornerstone see: