In this post here on possible cause why the discovery wizard could run forever. Last week I faced a situation where the discovery wizard for deploying Linux agents and for deploying windows agents didn’t work. The setup topology was 2 management servers SCOM 2012 and one dedicated SQL Server 2008 R2 SP1 for the SCOM databases.
If you want to know how much space your OperationsManger database is using you could run a SQL Report. Because it is a feature from SQL Server 2008 R2 it’s easily overseen I just want to show an example.