This can often be confusing once you read vendors' marketing materials. Simply stated, unified storage [or multiprotocol storage] refers to a single storage system that can support both file access and block access. That means I can use it for file systems and storing file data; or I can use an application that does block-based I/O right to that storage system. That [unified or multiprotocol] storage system is really operating in two modes: block and file.
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Go to the beginning of the Unified Storage FAQ Guide.