Cloud data transfers from Amazon Web Services to Microsoft Azure came out on top in a study into of the amount of time it takes to transfer 12TB of data from one cloud to another - and there can be up to a 25 times difference in transfer speed among providers.

Nasuni, which provides cloud storage using various public clouds, tested how long it took to transfer the data between Amazon Web Services Simple Storage Service (S3), Microsoft Azure and Rackspace. The company used 22 million files of mixed sizes, with each file having an average size of 550KB. Transferring into AWS from Microsoft Azure was the fastest and transferring data from AWS to Rackspace was the slowest.

For example, transferring from one bucket of AWS's S3 servers to another set of S3 servers took four hours. Transferring from S3 to Azure took 40 hours and transferring from S3 to Rackspace took 115 hours, or almost five days. Nasuni also tested data transfers into S3 and found that migrating the data from Azure to S3 took four hours and moving it from Rackspace to S3 took five hours. Nasuni did not perform Azure to Rackspace or vise versa testing.

There are some caveats to the study. Namely, Nasuni used AWS Elastic Cloud Compute (EC2) m1.large size computers to power the data transfer. The company admits that if Microsoft or Rackspace computers had been used, the results could be different. Factors such as the time of day when the transfer is occurring and the compute power of the machines running the transfer can also cause varying results, Nasuni pointed out.

"Enterprises must maintain flexibility and these tests demonstrate that," says Andres Rodriguez, CEO of Nasuni. "While data can be moved from cloud-to-cloud relatively quickly with some providers, others require an unacceptable amount of time to complete."

Nasuni's analysis follows a report in December evaluating 16 cloud service providers based on factors such as read and write speed, service uptime and scalability. In that test, AWS came out on top as well.