Network-attached storage (NAS) is file-level computer data storage server connected to a computer network providing data access to a heterogeneous group of clients. NAS not only operates as a file server, but is specialized for this task either by its hardware, software, or configuration of those elements

• File sharing refers to storing and accessing data files over a network. In a file sharing environment, a user who creates the file determines the type of access to be given to other users (read, write, execute, append, delete, and list) and controls changes to the file. When multiple users try to access a shared file at the same time, a protection scheme is required to maintain data integrity and, at the same time, make this sharing possible.

• The traditional client/server model, which is implemented with file-sharing protocols, is another mechanism for remote file sharing. In this model, the clients mount remote file systems that are available on dedicated file servers.

• Two common NAS file sharing protocols are:

1. NFS – Network File System protocol Traditional UNIX environment file sharing protocol

2. CIFS – Common Internet File System protocol Traditional Microsoft environment file sharing protocol, based upon the Server Message Block Protocol.

CIFS

• CIFS is client/server application protocol, which enables clients programs make requests for files and services on remote computers on the Internet. CIFS is a public (or open) variation on Microsoft’s Server Message Block (SMB) protocol. SMB is widely used on LANs. Like SMB, CIFS runs at a higher level than, and uses the Internet's TCP/IP protocol. CIFS is viewed as a complement to the existing Internet application protocols such as the File Transfer Protocol (FTP) and the Hyper Text Transfer Protocol (HTTP). The CIFS protocol allows the client to:

  i) Get access to files that are local to the server and read and write to them

  ii) Share files with other clients using special locks

  iii) Restore connections automatically in case of network failure

  iv) Use Unicode file names

  In general, CIFS gives the client user better control of files than FTP. It provides a potentially more direct interface to server programs than currently available through a Web browser and the HTTP protocol.

• CIFS runs over TCP/IP and uses DNS (Domain Naming Service) for name resolution. These file system protocols allow users to share file data across different operating environments as well as provide a means for users to transparently migrate from one operating system to another.

  1.File system is mounted remotely using NFS or CIFS protocol

  2.Application I/O requests transparently transmit data to the remote file system by the NFS/CIFS protocol. This is also known as redirection.

  3.Utilizes mature data transport (TCP/IP) and media access protocols

  NAS device assumes responsibility for organizing block level data (R/W) on disk and managing cache ensuring efficient management and data security.

• NFS and CIFS enable the owner of a file to set the required type of access, such as read-only or read-write, for a particular user or group of users. In both of these implementations, users are unaware of the location of the file system. In addition, a name service, such as Domain Name System (DNS), Lightweight Directory Access Protocol (LDAP), and Network Information Services (NIS), helps users identify and access a unique resource over the network. A naming service protocol creates a namespace, which holds the unique name of every network resource and helps recognize resources on the network.

NFS

• NFS is a client/server application that enables a computer user view and optionally store and update files on a remote computer as though they were on the user's own computer. It uses Remote Procedure Calls (RPC) to communicate between computers.

• The user's system requires an NFS client to connect to the NFS server. Since the NFS server and client use TCP/IP to transfer files, TCP/IP must be installed on both systems.

• Using NFS, the user or system administrator can mount all or a portion of a file system (which is a portion of the hierarchical tree in any file directory and subdirectory). The portion of the file system that is mounted (designated as accessible) can be controlled using permissions (e.g., read-only or read-write).