Last weekend I needed to move from one windows 2012 to another one. And I have a large website runs in IIS.
Normally in IIS manager you can export with web deploy tool. But I hit the 4gb max size limit. And the dialog was saying use archivedir.
Here is how you can do it. For backing up whole sites from your IIS
msdeploy -verb:sync -dest:archivedir=c:\site1archive,encryptPassword=password -source=webserver
After you move whole folder to new machine here is how you can import all sites into fresh new IIS
msdeploy -verb:sync -dest=webserver -source:archivedir=c:\site1archive,encryptPassword=password