Hi Jzhao,
The best solution here is to look at site replication, this works by storing the file data in one database on one site (US Server) and then "replicating" the filetore at both sites.
In most cases you would set the Vault to replicate overnight (or window between US finishing and you starting the day) so when you start work you have all the latest files locally - no need to copy them across the network live. (It will resolve missing files between the sites on demand as well)
Unfortunately this functionality is ONLY AVAILABLE in Productstream, NOT Vault, you should speak to your reseller about what is involved in order to move to this type of system.
Hope this helps,
Allan (Autodesk)
Allan
Product Manager
Autodesk, Inc.