The SharePoint 2010 capactity planning document states that a database for a single sitecollection should not exceed 200 GB. However, if I use SQL Server RBS I can keep the physical database size easily below that limit but the size of the 'virtual' database (physical database and blobstore) will be in the TB's range. Do I need to keep my 'virtual' database size below the 200 GB limit, or will performance be okay if just the physical databse is below the 200 GB limit?
Basically yes, that includes everything (blob storage). You can go over that limit, but there are some very specific requirements if you do.
Take a look at the requirements in these links:
Here is the key part:
Content databases exceeding 200 GB and up to 4 TB support much of the same flexibility as content databases <200 GB. However, additional planning should be considered in order to effectively manage those databases in respect to operational and hardware considerations.
Another good link here, especially the point regarding RBS and content database limits.
We are clarifying that Remote Blob Storage (RBS) does not offer a way to increase the SharePoint content database size limits. The content database supported size limits apply to the sum of data stored in SQL Server plus data stored outside of SQL Server using an RBS provider. A description and the value of RBS is detailed in the team blog post.