As technology evolves over time, distinctions become blurred as manufacturers try to add in features supported by other products to extend their product lines and reduce obstacles to sales. We are at the beginning of this for SANs and NAS. Essentially the objects you reference are the same, something that works like a SAN on the backend but looks to the network like a NAS (doesn't require a connection through a host). The software provided in each case is up to the manufacturer.
While each situation is different and has unique costs and benefits, your overriding rule should be to beware of proprietary solutions.
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