I don't think that "all" storage systems will be unified [a.k.a. multiprotocol]. I do think you'll see a unified offering from all the major vendors because it's a very competitive world, and to not have an offering might be perceived a weakness or limitation on the vendor's part. But there are reasons to avoid unified storage; especially in cases where granular control needs and high performance requirements necessitate block-based storage. You'll continue to see independent block and file offerings. You will probably see file-based products that can be utilized as "NAS-only," or support an optional block-mode interface for unified storage; that will probably be the trend into the near future.
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Go to the beginning of the Unified Storage FAQ Guide.