Just thought I would qualify something, as I have been asked this a few times of late, and sometimes by people whom I would have expected to have understood this...
Within SharePoint (v2 or v3) the lowest ratio of content DB’s to Web Applications (virtual servers in v2) is 1:1
- You have multiple content DB’s for a given web application.
- You can have multiple site collections in a web application.
- The lowest ratio of content DB’s to site collections is 1:1
- You can have multiple site collections in a given content DB (recommended max is 50k – performance drops off after 50k, it isn’t a hard limit)
- By default you only get 1 content db when you create a web application, you can add more from http://sca:port/_admin/cntdbadm.aspx (SCA > AppMan > Content DB’s) or from STSADM.
Where you have multiple content DB’s for a given web application, SharePoint will distribute site collections across the content DB’s.
Let’s say you had 3 content DB’s for a web application (DB1, DB2 and DB3).
The first site (say a Portal/Intranet at root) will go into DB1.
When you create new site collections (these must be collections NOT sub-sites/webs of the “root” Portal) they are distributed (round robin style) to the other content DB’s based on the order of priority (basically the order the content DB’s were created in) and by the number of sites in the content DB’s.
So, “site-A” goes into DB2, “site-B” goes into DB3, “site-C” goes into DB1, “site-D” goes into DB2, round and round we go (like a card dealer!).
The logic is not present to distribute site collections based on any attribute (URL path, metadata etc) or size.
You could end up in a situation where you have multiple contents DB’s (say 3) but due to bad luck all the large collab spaces end up in DB1. Therefore you will have a even distribution (numerically) of site collections across the content DB’s but DB1 will be huge while DB2 and DB3 will be small.