As far as i know you can use any database for your metric store. Just take in consideration where your data is coming from. An other thing we encountered was that you need to get a unicode based databse (that's where we went wrong :-[)
QuoteDo we need to create a separate database for this or conent store itself can be used.
Just to be clear the Metric Store and the Content Store are completely seperate.
A Metric Store is used to store your metric data based on the calendar parameters you have set when you initially created the Metrics Package.
Unlike the content store which is a repository the Cognos tool uses to run the Metric Store will actually hold data values.
Additionaly if you have multiple Metrics Packages built based off of different rules, different data or even a different time frame can have multiple metric stores but still only a single content store.
It's a bad analogy so please forgive me in advance ::)
A Metric Store could be viewed similar to a Cognos Cube. If you have like Data you can meet several different reporting requirements in a single location. But if the Business Rules or Time base or data is too different you will be forced to build a second Metric Store and Metric Package the same way you would have to build a seperate cube.
So if your looking at building your first Metrics Package I highly recommend you spend a good bit of time in the Analysis and Design phase and set the Metrics Package up accordingly.