We’ve all set up test vCenter installations and used the built-in Microsoft SQL Server Express engine. It is a great way to get up and running to test this or that feature of vCenter before trying it in production. For a production environment, I’ve always preferred to leverage a shared (or centralized) SQL Server to host the database. Primarily, they are easier to manage across all database installations (for topics such as SQL Server updates and service packs). As a secondary benefit, there is less overhead in having a number of virtual machines provisioned with extra memory and CPU resources dedicated to having multiple SQL Server Express installations running around.