A site  collection must reside completely in one Content Database. Your
only choice is to break up the site collection. If you're interested in
that I could write something up.

I know that many people would be interested in what you have to say
about breaking up a site  collection. We have some extremely large site
collections and would like to know how to split them up over several
databases. Is it possible to preserve the current urls?

For V2, you would have to SMIGRATE the site  (subweb) out, then use something
to “Replay” the permissions back onto the site.

(See: “Replaying Permissions and Moving Webs”
blogs.msdn.com/.../687850.aspx )

For V3, you can use STSADM –o export/import to move the site(subweb) around
without needing to reply the security (There is an includesecurity switch)

In the end, for both versions, you can’t maintain the web hierarchy of a
single site collection  across databases. A site collection can only live in
one database as mentions below.

So, if you had something like:

http://server/sites/topsite/bigolsubweb/someothersite

And you wanted to move the subweb “bigolsubweb” to a different database, you
would have to

1. export it out (including someothersite and all others)

2. Provision a new site collection in a new database (I can send you
instructions for specifically targeting one if you need)

3. Import “bigolsubweb” into the new site collection.

Keep in mind, that “bigolsubweb” would either need to be a new top level
site now, or a child of something else in that new site collection.

What I’m saying, is that you can’t have the “topsite” portion in one
database, “bigolsubweb” in another, and even “someothersite” in another.

Most folks that have wanted this, always want to maintain the web hierarchy
of where their current web resides, which just can’t be done

Does that make sense?

I'd second that...knowing what the options are when it comes to a
single collection  getting very large would be helpful.

Sounds like there's some interest. I'll start writing something up for my blog.
Stay tuned.

I guess I wasn't clear. First, like I said a Site Collection MUST reside
completely in one Content Database. No exceptions. Your only choice is to
break the Site Collection up into multiple Site Collections and put them in
seperate databases. I suppose it's possible to maintain the URL structure, it
would take some work and planning  though.

See the details with screenshots
mysharepointwork.blogspot.com/.../...ons-into.html