See this as well.
Top 10 Symantec Best Practices - Deploying Symantec Endpoint Protection Architecture
http://www.symantec.com/business/support/index?page=content&id=TECH92051&actp=search&viewlocale=en_US&searchid=1290018469744
Note # 9. If utilizing MS-SQL for the SEPM database, it is preferable to run this on a physical machine (as opposed to a virtual machine).
- This will ensure less chance of Disk I/O and other resource bottlenecks