One of the main reasons it has been difficult to achieve meaningful openness in the SAN market is simply due to the complexity of the technology. Ethernet and IP networks assume intelligence on the part of end systems (nodes), with the network itself largely restricted to data transport. SANs assume intelligence in the network (the fabric) and little intelligence on the end systems (particularly storage targets). Designing a new fabric switch or host bus adapter that is both standards-compliant and interoperable is therefore far more challenging than in the data communications world.
In addition, although storage targets may have lower IQs than the fabric they're attached to, they are a much higher expense and as a result tend to be a much higher priority for customers. For a switch or adapter to achieve success in the SAN market, for example, it must have stamps of approval from the storage systems providers. This has the practical benefit of openness, in that different products are qualified and supported to work together. But this is not open systems by IP and Ethernet expectations.
With its CLARiiON-based SAN Copy data copy application, EMC has made a significant step towards accommodating heterogeneous storage without the use of virtualization appliances. These sorts of solutions are predicated on previously established standards for initiator and target behavior, and as long as customers have the flexibility of using a diversity of products to accomplish common tasks, the solutions have the look and feel, if not the reality, of openness.