Online retailer Amazon is to add persistent storage features to its Elastic Compute Cloud (EC2) hosted service, making it more reliable.

The new features, available later this year, will provide persistent storage volumes that will exist independently of any Amazon EC2 instances, effectively behaving like "raw, unformatted hard drives", the company claimed. Users will be able to create volumes ranging in size from 1 GB to 1TB.

Previously, users had been able to allocate as much as 1.7TB of attached storage to the virtual machines they were running, but as soon as the instance was shut down, the storage disappeared.

In a letter to EC2 customers, Amazon promised: "This feature will make it even easier to run everything from relational databases to distributed file systems to Hadoop processing clusters."

So far, cloud computing services have mainly appealed to web-based start-ups, but the addition of more enterprise-class features will widen the appeal.

As Dan Hubbard, chief technology officer at internet security firm Websense explained, the ability to tactically deploy virtual machines capable of running an entire operating system for a few pounds is extremely attractive for short-term projects.

Nevertheless, the cloud computing services also raise security concerns, he noted, with network managers uncertain about what data resided on these virtual machines. "From a security point of view, all I see is web traffic. That's pretty frightening," he said.