When designing a system the question of how much space do I need for the databases always comes up. With MOM 2005 there was a spreadsheet provided my Microsoft to help. For 2007 Microsoft expects you to use System Center Capacity Planner which is still in beta. As well as not being finished SCCP only tells you the number of drives of a specific size that you need like 3 x 72 GB and not an actual figure. This helps but a real figure would be nice.
Kerrie and Cameron have done some great work to help with sizing the SCOM databases. http://ops-mgr.spaces.live.com/Blog/cns!3D3B8489FCAA9B51!171.entry. I wrote a post showing how to turn it into a spreadsheet at http://ianblythmanagement.wordpress.com/2007/06/06/database-size-estimation/.
I developed the spreadsheet for my own use and thought that if I find it useful then so would other people so I tidied it up and Pete kindly put it up on System Center Forum.
http://systemcenterforum.org/operations-manager-database-size-estimator/ or you can download it directly at http://systemcenterforum.org/wp-content/uploads/SCOM2007DBestimatorv1.xls.
I have tried to make it simple and easy to use – just put in the number of agents! I have also made sure everything is parameterized so you can alter the assumptions made like the MB/day if you have more MPs or the groom days if you have changed that setting.
Hope you find it useful.