When engineers perform calculations to see what the result of some particular action will be, they are actually working with a model of a physical system. Modeling is essential to describe any kind of physical system, and storage networks are no exception. So in an effort to make it easier to understand, design, and even talk about storage networks, the Storage Networking Industry Association (SNIA) has developed a model to describe storage networks of all types. If this storage model becomes as popular as the OSI model for describing networks of all kinds, it will be a major communications aid for storage administrators.
Like the OSI seven-layer model for communications and networking, the SNIA Shared Storage Model (SSM) is descriptive, not proscriptive. It is designed to provide an architecture- and vendor-neutral way to look at storage networks of all types, not just SANs. It divides a storage network into layers and lets users, vendors and others talk about storage networks using standard terms that (it hopes) will be less subject to "meaning creep" and "term inflation".
The SSM uses a four-layer model with the application on top (layer IV) and the physical devices on the bottom (layer I). Beneath the application layer is the file/record layer (layer III) which handles database and file system functions. Below the file/record layer is the block aggregation layer (layer II), which provides services such as space management, redundancy and striping.
The model is described more fully in a white paper on the SNIA web site at: www.snia.org/English/Collaterals/Whitepapers/Shared_Storage_Model.pdf.
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.