There is a need to predict "how much storage SharePoint will need over the next 3 years" so that systems administrators can plan for the future. Unless historical data in the way of "size snapshots” or SharePoint farm has been kept, there is no easy way to answer this question.
ControlPoint’s Storage Trend Analysis report can be set to summarize the farm’s changes in storage over a specified period of time and present it in an easy to read graph. In the sample report below, you can see that the farm is showing a consistent upward growth trend, which could be projected into the future. For further information on analyzing trends, please click here.
