Some vendors also offer private connections established from the enterprise to one of the provider's storage nodes. This is well suited for companies with initial data sets between 2TB and 75TB, or fewer than 750 million files, and where data transfer is time-sensitive, according to Nirvanix Inc., a San Diego-based cloud storage provider. It also works well for one-time and ongoing data migration that requires high throughput and moderate latency.

The other option -- most often used by enterprises -- is the "sneakernet" approach, where data is physically picked up from the customer on a disk, tape or appliance provided by the cloud storage provider, and taken to the data center for initial backup.

"We've had customers that have shipped storage arrays," says Jon Greaves, chief technology officer at private cloud host Carpathia Hosting Inc. in Ashburn, Va. "In some cases, customers have physically removed disks from the chassis after they have been mirrored, and delivered those."

Nirvanix, for instance, will send its customers storage servers with dual Gigabit Ethernet ports to transfer data within their own facilities. Once the data is transferred, the servers are sent back to Nirvanix and the data is migrated to the cloud.

Amazon Web Services LLC supports moving large amounts of data into and out of its cloud using portable storage devices. It uses a high-speed internal network to transfer customer data directly onto and off of storage devices, bypassing the Internet.