How big is ETL effort? – 70%
According to the book The Data Warehouse ETL Toolkit:
The ETL system makes or breaks the data warehouse. Although building
the ETL system is a back room activity that is not very visible to end users,
it easily consumes 70 percent of the resources needed for implementation
and maintenance of a typical data warehouse.
Of cause ETL is not only used in data warehousing project. ETL is also commonly used in Data Integration project. According to statistics, ETL typically takes up between 50 and 70 percent of a data warehousing or data integration project.
In the current data integration project I am working on with a large client, there are 3 full time ETL designers/developers on the project, together with total 11 team members, including 2 project managers.