What is NAS (Network-attached Storage)?

NAS is a single device, sharing its own storage over the network. Unlike SAN, NAS appears to the server as an external storage device. The main downside of using NAS is its performance issue and its dependency on the network, which is also used for normal traffic, resulting in congestion. When a server sends a file read/write request to NAS, it is sent in form of a network file system (NFS) command. NAS has to convert this into the local storage I/O command set, leading to delays. NAS uses ethernet as the primary media with NDS being the main I/O protocol.