Network attached storage (NAS) differs from the traditional file serving and Direct Attached Storage (DAS) in that the operating system and other software on the NAS unit provide only the functionality of data storage, data access and the management of these functionalities. Furthermore, the NAS unit does not limit clients to only one file transfer protocol. network attached storage systems usually contain one or more hard disks, often arranged into logical, redundant storage containers or RAIDs (redundant arrays of independent disks), as do traditional file servers. NAS removes the responsibility of file serving from other servers on the network and can be deployed via commercial embedded units or via standard computers running network attached storage software.
NAS uses file-based protocols such as NFS (popular on UNIX systems) or SMB (Server Message Block used with MS Windows systems). Contrast NAS's file-based approach and use of well-understood protocols with storage area networks SAN which uses a block-based approach and generally runs over SCSI, Fibre Channel or iSCSI.
The boundariess between network attached storage and storage area networks systems are also starting to overlap, with some products making the obvious next evolution and offering both file level protocols (Network attached storage) and block level protocols (Storage Area Networks) from the same system. An excellent example of this is Openfiler the open source product running on Linux
ManageEngine OpStor monitors even network attached storage devices like NetApp filers and provides information about their storage infrastructure, assets, performance and fault management