Once the data warehouse goes production, it needs to be maintained. Tasks as such regular backup and crisis management become important and should be planned out. In addition, it is very important to consistently monitor end user usage. This serves two purposes: 1. To capture any runaway requests so that they can be fixed before slowing the entire system down, and 2. To understand how much users are utilizing the data warehouse for return-on-investment calculations and future enhancement considerations.
Consistent availability of the data warehousing system to the end users.
Usually by this time most, if not all, of the developers will have left the project, so it is essential that proper documentation be left for those who are handling production maintenance. There is nothing more frustrating than staring at something another person did, yet unable to figure it out due to the lack of proper documentation.
Another pitfall is that the maintenance phase is usually boring. So, if there is another phase of the data warehouse planned, start on that as soon as possible.