When comparing SAN vs. NAS or iSCSI, it's often a matter of block vs. file. To support block transfers, run Fibre Channel (FC), FICON, FCIP, iSCSI. For file transfers, use NAS with CIFS or NFS. Block transfers offer low latency and high performance; mainly for applications that require block transfers. For example, some applications can run on NAS but may perform better under different workloads. Common examples include databases and Microsoft Exchange. There are caveats, and you can run applications in different modes if you follow the vendor's recommendations. Some Microsoft applications can run on NAS as long as it's a Microsoft-based file system. This puts many NAS vendors at a disadvantage unless they're running a Microsoft file system. Ultimately, run NAS when you need to share data. If you need to share your storage over the network, that's an ideal application for NAS. This is also true if we need to share a file.
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