Amazon Web Services, the public-cloud business of Amazon.com, has launched an enterprise cloud storage service that can be used by companies’ on-premise applications.

The AWS Storage Gateway stores data onsite but replicates it to Amazon’s cloud asynchronously, lending itself well to be used for disaster recovery.

Alyssa Henry, general manager of AWS Storage Services, said the gateway provides yet another way enterprises can use the company’s storage cloud. “The AWS Storage Gateway works with your existing applications using a standard iSCSI interface, securely transfers your data to AWS over SSL, and stores data encrypted at rest in Amazon S3.”

Enterprise cloud storage is a busy and rapidly growing space, populated by both long-established high-tech firms and start-ups. Amazon is among leaders in the space with its Simple Storage Service (S3), competing against start-ups like Nirvanix and Box.net and old-timers like EMC, NetApp and IBM, among others.

Companies will often partner and combine technologies to deliver cloud storage solutions. Amazon has the resources to do it on its own.

IBM and Nirvanix, for example, formed a partnership in October 2011, integrating Nirvanix’ cloud storage technology with IBM’s SmartCloud Enterprise storage services, which delivered IBM’s global customer base to Nirvanix.

The IBM/Nirvanix partnership is a very strong competitor to Amazon in the space. Nirvanix is a highly recognized cloud storage provider, and IBM’s global infrastructure gives its customers the choice of uploading their data to multiple locations anywhere in the world.

These global multi-site storage capabilities are also one of Amazon’s key strong suits.

The advantage of using Amazon’s new storage service is seamless integration between on-premise applications and the public Cloud. Because it uses industry-standard storage protocols, the integration is instantaneous. There is no need to re-architect existing applications.

It works by installing a piece of software – the gateway – at the customer’s data center and dedicating some storage capacity on traditional data center hardware for its use. This is to ensure performance for latency-sensitive applications. The gateway stores data on premises but also asynchronously replicates it to S3.

Another advantage, according to Amazon, is the ease of using this data with its compute cloud service called Elastic Compute Cloud (EC2), which provides on-demand compute capacity.