The Storage Network Industry Association's (SNIA) Shared Storage Model (SSM) is one of the most important emerging storage standards of the decade. You need to know about this standard, even though you'll never be able to buy an SSM product or use the SSM architecture.
The importance of the shared storage model is that it's an industry-standard model of storage architectures and the way their pieces fit together, backed by a common vocabulary and definitions of terms. The goal of the SSM is to provide common ground for manufacturers, customers and others to define and discuss storage systems. It also lets manufacturers clarify the differences in their products and customers better understand what vendors are offering. As a result SAN administrators are going to be hearing a lot about the SSM and will need to understand the model and its vocabulary.
Neither is particularly difficult. Like the OSI network model, the SSM is divided into layers with the application sitting at the highest level. The storage and associated networking and services are referred to as the storage domain. The next level down from the application (and the top level of the storage domain) is the file/record layer, which includes database and file system components.
Below that comes the block aggregation layer (if the storage is networked), which includes the host, network and device layers. The storage devices are below that and at the very bottom is the block layer, which includes features for space management, striping and redundancy. Sitting off to the side, as it were, are services such as discovery. Tying all this together is a well-defined system of interfaces and networks that are designed to promote interoperability among equipment from various vendors.
The SSM is still a work in progress and it is currently being extended to include things like tape drives and data movers. However even in its present state it is a valuable tool for understanding storage architectures. SNIA has an overview of the Shared Storage Model.
Rick Cook has been writing about mass storage since the days when the term meant an 80K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last twenty years he has been a freelance writer specializing in storage and other computer issues.
