Offline disk import gives you an option to load data into Google Cloud Storage by sending Google physical hard disk drives (HDDs) of data which we load on your behalf. Using this option can be helpful if you're limited to a slow, unreliable, or expensive Internet connection.
To use offline disk import, write your data to HDDs and then ship the HDDs to a Google import center using a mail carrier. For security during shipment, the data on the HDDs must be encrypted. Upon receiving the HDDs, Google uploads the data into an empty Cloud Storage bucket that you designate. Because the data is loaded directly into Google's network, this approach might be faster or less expensive than transferring data over the Internet.
Read more: Google developers