Mention cloud storage to most IT professionals and they think of Internet services like Amazon S3 and Nirvanix that store your data in their data centers.
But a storage cloud doesn't have to be public. A wide range of private cloud storage products have been introduced by vendors, including name-brand companies such as EMC, with its Atmos line, and smaller players like ParaScale and Bycast. Other vendors are slapping the "cloud" label on existing product lines. Given the amorphous definitions surrounding all things cloud, that label may or may not be accurate. What's more important than semantics, however, is finding the right architecture to suit your storage needs.
A prototypical cloud storage system is made up of a number of x86 servers, each with its own storage, most commonly using four to 16 SATA drives. Users and their applications access the system through standard file access protocols like CIFS and NFS or via object storage and retrieval protocols like SOAP and REST.
The storage nodes in a private cloud are linked together with a layer of smart software, which performs several functions. First, it maintains a global name space that allows all the storage in the cluster to be accessed as a single entity, so that administrators can add storage capacity on the back end without having to tell applications at the front end how to reach it. The software also handles drive failures and keeps data available to applications and end users.
A private cloud storage infrastructure should also be able to scale from hundreds of terabytes to multiple petabytes. That level of scalability is achieved not with a forklift upgrade, but simply by adding more servers as they're needed.