Introduction to Unified NAS & IPSAN in Comparison with FCSAN
Approach towards networked storage started in the 1980s with the introduction of Network Attached Storage devices and continued later in the 1990s when Fibre Channel (FC) emerged as an alternative method of connecting storage. FC could be used in either a loop technology, with up to 126 devices attached to a loop, or in a fabric with switches connecting multiple file servers and storage devices. This removed the direct connection between file servers and storage, allowing storage to be networked with multiple file servers sharing storage devices on a Storage Area Network (SAN).
Network Attached Storage:
Network storage was developed to address the challenges inherent in a server-based infrastructure such as direct-attached storage. Network-attached storage, or NAS, is a unique purpose device, comprised of both hard disks and management software, which is entirely dedicated to serve files over a network. As we are aware that, a server has the dual functions of file sharing and application serving in the DAS model, potentially causing network slowdowns. NAS relieves the server of storage and file serving responsibilities, and provides a lot more flexibility in data access by virtue of being independent. Another important consideration for a medium sized business or large enterprise is heterogeneous data sharing. With DAS, each server is running its own operating platform, so there is no common storage in an environment that may include a mix of Windows, Mac and Linux workstations. NAS systems can mix into any environment and serve files across all operating platforms. On the network, a NAS system appears like a native file server to each of its different clients. That means that files are saved on the NAS system, as well as retrieved from the NAS system, in their native file formats. NAS is also based on industry standard network protocols such as TCP/IP, FC and CIFS.

Background of IP-SAN:
A SAN is a network that connects file servers and storage devices. A SAN storage device is a block-structured storage device, serving blocks to a file server. The most important thing about a SAN is that it separates the storage from servers, allowing the storage to be utilized and managed in much more effective way than with DAS. This allows storage to be consolidated in storage pools and allocated to file servers, as needed.
Instead of a systems manager having to take a server down to deal with a failed disk or a server that has run out of space, with a storage network servers can be provided with virtual disks with built-in redundancy and the ability to grow as the demand for capacity grows. Unlike a Direct Attached environment, storage can be added to a SAN without server downtime and disruption. Separating storage from servers also enables highly available systems with no single point of failure to be developed. If a file server fails, another can easily take over its storage, and if storage is mirrored on the SAN, a file server can easily connect to a mirror of

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