A Microsoft TechNet Wiki "How to shrink your SCVMM database (Transactional Log)" is published by Microsoft Partner and MVP Leandro E. Carvalho. This one discusses how to manage the size of your VirtualManagerDB_log:
Ok, you have had your SCVMM server running for a while now, all roles and services installed on a single server. Remember that the SCVMM 2008 R2 server installs a SQL 2005 Express if you don't specify another instance for this purpose. The storage limit for a database in SQL 2005 Express is 4GB, so what do you do when the VirtualManagerDB_log starts to grow out of control?
First, we have to locate our databases.