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For example, the focus clearly is on low cost and easy scalability. "There's a big financial aspect to storage clouds" said Anand Prahlad, CommVault's vice president of product development. "Not only is it expected to be low cost, but you pay only for what you use." Simply put, internal storage clouds are expected to deliver cheap storage.
And not only cheap storage, but slow as well. Consultants like Schindler, however, don't rule out better storage performance or different service levels as part of the internal storage cloud.
Manageability represents another distinguishing factor. "With an internal storage cloud you want to abstract away the complexity of the storage," said David Allen, chief technology officer (CTO) at i365, A Seagate Company. As a result, the private storage cloud should be easier to manage, enabling a single administrator to handle hundreds of nodes and petabytes of storage. However, the administrator's responsibilities may be limited to a handful of simple tasks.
Finally, how the private storage cloud is accessed can be a key distinguishing factor. HTTP will be the dominant access protocol. "All you want is HTTP or HTTPS connectivity and a Web browser," suggested Ken Satkunam, CTO at SentryBlue in Fargo, N.D.
"A big difference with the internal storage cloud is that it's accessible through
an API, not a protocol," Nirvanix's Foskett said. "It will have a programmable API just like a website, maybe use REST over HTTP." Representational State Transfer (REST) is a stateless protocol that includes the state with every communication, the opposite of Fibre Channel (FC). REST provides access to Web services using HTTP; for storage clouds, REST would be used to access storage resources as services.
In a recent whitepaper, Sun Micro-systems Inc. insists on this type of programmability in the storage cloud. "Instead of physically deploying servers, storage, and network resources to support applications, developers specify how the same virtual components are configured and interconnected, including how virtual machine images and application data are stored and retrieved from a storage cloud. They specify how and when components are deployed through an API."
But the industry hasn't standardized on a cloud API, StorageIO Group's Schulz noted, and every cloud provider offers its own. In late July, however, Rackspace Hosting made the API specifications for its public Cloud Servers and Cloud Files open under the Creative Commons 3.0 Attribution license. This might eventually give would-be internal storage cloud builders an open API to get started.
One final characteristic -- multi-tenancy -- defines the public storage cloud. "Multi-tenancy is an important part of the storage cloud and even the internal storage cloud," CommVault's Prahlad said. With internal or private cloud storage, multi-tenancy would let the organization separate departments, projects and workgroups as needed.
So what is an internal storage cloud? The consensus definition appears to be private storage capacity owned or at least controlled by the company, accessible programmatically over an HTTP connection and capable of delivering low cost, highly scalable storage with easily managed multi-tenancy. ParaScale Inc. adds that an internal storage cloud can be small (as few as three to five nodes), and still deliver the economies of cloud storage as well as the ease of management and scaling associated with the cloud.
This was first published in October 2009