For a lot of NAS-based systems -- even Windows Storage Server (WSS) with an iSCSI target -- unified storage capability is probably not significantly more costly than a basic NAS system; maybe just an added charge for extra software. If you look at the block-based storage systems, they're typically more expensive because there is more specialized hardware and they're tuned for higher (and more consistent) performance. There is actually a bit more expense for block-based platforms that have added another interface card to support NAS because the NAS adapter is specially designed to suit the block platform. Comparing block and file storage systems that are generally available today, the file-based (NAS) systems are typically less expensive because they're simpler and easier to understand.
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