There are two methods of getting around this. In the first method, the administrator goes to all Content Databases (SharePoint Central Admin – Application Management Tab – Content Databases) and takes the databases ‘offline’. Note that simply taking the databases offline does not affect user functionality; it only dissallows new Sites from being created in the specific Content Database. Once all Content Databases except for the one desired are taken offline, creating a new Site Collection will force that Site Collection to be created in the one you want.
If the databases aren’t created in advance, there is an even easier way to do this, by using the –createsiteinnewdb flag with the STSADM tool. The STSADM tool (located on web front-ends in the \program files\common files\microsoft shared\web server extensions\12\bin folder) is a fantastic administrative tool that performs a myriad of administration with SharePoint. In this case, it allows you to create a new Site Collection within a new Content Database. The following Syntax illustrates one example:
stsadm -o createsiteinnewdb -url http://docs.companyabc.com/dept/hr -owneremail SharePoint@companyabc.com -ownerlogin COMPANYABC\SPAdmin -sitetemplate sts -title “Human Resources” -databaseserver SERVER1 -databasename “HR-Content-DB”
In this example, a new site collection is created at the URL http://docs.companyabc.com/dept/hr. The Site Collection Owner is set to COMPANYABC\Spadmin and the Site Collection owner email is set to SharePoint@companyabc.com. The default team site template is used to create the site (the template is simply named ‘sts’, without the quotes.) The database server is SERVER1 and the name of the database created is HR-Content-DB.
Using this concept, you can construct a SharePoint environment that will scale quite nicely, as content is distributed across multiple databases. In addition, If you need to scale to multiple database servers, it simply involves moving content databases to the new server and updating the location in SharePoint.