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The Storage Networking Industry Association (SNIA) has announced the first cloud storage standard, the Cloud Data Management Interface or CDMI.

It provides "the means to access cloud storage and to manage the data stored there". Cloud storage is defined as the delivery of virtualized storage on demand over a network, also known as Data Storage as a Service (DaaS). Customers pay based on the actual stirage consumed.

The SNIA says that any storage delivered on a basis of fixed capacity increments is excluded from its definition of cloud storage.

The CDMI supports both block (LUN or virtual volume) and file (file system accessed by CIFS, NFS or WebDAV) legacy storage clients. The underlying storage space to both is abstracted as a container.

However, it can also be abstracted as a simple table storage space for database operations. The emphasis here is on scalability rather than features. It is not based on virtualised relational database (RDBMS) instances. Each RDBMS has its own proprietary interface, and the CDMI does not even attempt to offer a way of accessing a virtualised RDBMS in the cloud.

The SNIA states: "Due to the rapid innovation in this space, it is probably best to wait for further development of this type of cloud storage before trying to standardize a functional interface for this type of storage."

There is a fourth storage abstraction which is for objects, which treats objects as unique items accessible through a URI (Uniform Resource ID). In a possibly deliberately humorous acronym, the CNIA says data objects are dealt with as separate resources each created, retrieved, updated and deleted using CRUD semantics - what a delightful image.

With objects the containers can contain other containers.

The SNIA Storage Industry Resource Domain Model (SIRDM - the SNIA loves initialisms if you hadn't already guessed) provides a framework for dealing with metadata in the cloud. There is detail on how data stored in the cloud is managed and much more.

The CDMI is a straightforward specification that enables most legacy non-cloud storage product access methods to develop into cloud storage ones. It should provide a way for cloud storage to be embraced by data centres. Their access to an existing networked storage resource should be switched fairly easily and transparently to a CDMI cloud storage resource instead.

The SNIA has moved quickly to develop this standard and we can safely assume cloud storage offerings will quickly become CDMI-compliant. Perhaps the ones that don't can be thought of as CRUD and discarded.

What the CDMI does not do is provide a way to verify the quality of cloud storage suppliers in terms of reliability and quality. It won't prevent the Microsoft Danger kind of data loss or the like.

Still, it should help customers switch from one CDMI-compliant cloud storage supplier to another. The SNIA is not a trade body policing its members in the interests of delivering a quality service to customers. It is a trade body helping its members work together such that, hopefully, customers can use SNIA members' products hetereogeneously where that makes sense, and switch between them if they wish. ®

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