The two big differences between NAS and Fibre Channel SAN are the wires and the protocols. In terms of wires, NAS runs on Ethernet, and FC-SAN runs on Fibre Channel. The protocols are also different. NAS communicates at the file level, with requests like create-file-MyHomework.doc or read-file-Budget.xls. FC-SAN communicates at the block level, with requests over the wire like read-block-thirty-four or write-block-five-thousand-and-two.
If you think the protocol is more important, then iSCSI is like SAN; if the wire is more important, then iSCSI is like NAS.
Technical people know that the protocol is more important; it determines how the compute server talks with the storage. With FC-SAN, a filesystem like UFS, VxFS or ZFS runs on the host and converts file requests into the block requests that are sent over the wire. With NAS, the host sends file requests over the wire, so a filesystem must run in the storage system. There are advantages and disadvantages to both approaches, but the point is that from an architectural perspective, iSCSI looks just like FC-SAN. The filesystem runs on the host and sends block requests over the wire. (Many technical people are offended by the idea that iSCSI might be NAS.)
Business people focus on infrastructure, budgets, and org charts, so they worry about wires. Choosing NAS over SAN for Oracle, Exchange, or SAP affects the capital budget for Ethernet versus Fibre Channel, and it can even affect organizational structure. Sometimes an “Apps/Servers/Storage Group” owns Fibre Channel, while Ethernet belongs to a “Distributed Infrastructure Group”. Is the Apps group allowed to buy and manage their own Ethernet switches if they decide to run Oracle over NAS? They may argue, “We should own the switches between server and storage.” The Distributed Infrastructure group may argue, “We own all TCP/IP networking,” but the corporate network may not offer the bandwidth or quality of service required for Oracle-on-NAS. I’ve seen CIOs do reorgs over these issues. Business-wise, iSCSI looks just like NAS, so business people often assume that iSCSI is a form of NAS.
Credits : Article by – Dave