One huge db vs many small dbs

Hello,

We are starting a new project to deploy a solution in cloud with the possibility to be used for 2.000+ clients. Each of this clients will use several tables to store their information (our model has about 500+ tables but there's less than 100 core table with heavy use). Also the projected ammout of information per client could be from small (few hundreds tuples/MB) to huge (few millions tuples/GB).

One of the many questions we have is about performance of the db if we work with only one (using a ClientID to separete de clients info) or thousands of separate dbs. The management of the dbs is not a huge concert as we have an automated tool.

At Google there's lots of cases about this subject but none have a scenario that matchs with the one I presented above, so I would like to know if anyone here has a similar situation or knowledgement and could share some thoughts.

Thanks

Max