Questions about DBDOWNLOAD

Hi,

Could anyone give me more information about what's going on behind the scenes when using the server/mirrorsync/dbdownload/UID functionality?

Is the target databased directly downloaded or is a copy created on the server first. If a copy is created, where is this filed (temporarily?) stored and is there a way to change this location?
Is there a way to make that copy structure only as opposed to structure + data?

Might have follow up questions. Many thanks in advance for any information or links to relevant resources.

Nils