Network Attached Storage (NAS) is a file-level storage architecture where 1 or more servers with dedicated disks store data and share it with many clients connected to a network. NAS is 1 of the 3 main storage architectures along with storage area networks (SAN) and direct-attached storage (DAS) and is the only 1 that’s both inherently networked and fully responsible for an entire network’s storage.
Compare NAS to more familiar storage volumes, like your PC’s hard drive, external drive, CD, or USB flash drive. A NAS architecture allows you to store and share file-based data, much like any storage volume. But while your hard drive, external drive, CD, or flash drive can only connect to 1 device at a time, NAS is networked to support many devices simultaneously.
Network Attached Storage units are built to serve data as files. Although they’re technically able to complete general server tasks as well, NAS units run software that protects data and handles permissions—that’s it. This is why NAS units don’t need a full-featured operating system. Most NAS units contain an embedded, lightweight operating system fine-tuned for data storage and presentation.
To present these files, a NAS unit uses standard file-based protocols, such as Network File System (NFS), Server Message Block (SMB), Common Internet File System (CIFS), and/or Apple Filing Protocol (AFP) which are the protocols used to communicate with Linux® and UNIX, Microsoft Windows, and Apple devices, respectively.
The main benefits of Nework Attached Storage include:
- Scale out capacity: Adding more storage capacity to NAS is as easy as adding more hard disks. You don’t have to upgrade or replace existing servers, and new storage can be made available without shutting down the network.
- Performance: Because NAS is dedicated to serving files, it removes the responsibility of file serving from other networked devices. And since NAS is tuned to specific use cases (like big data or multimedia storage), clients can expect better performance.
- Easy setup: NAS architectures are often delivered with simplified scripts, or even as appliances preinstalled with a streamlined operating system, greatly reducing the time it takes to set it up and manage the system.
- Accessibility: Every networked device has access to NAS.
- Fault tolerance: NAS can be formatted to support replicated disks, a redundant array of independent disks, or erasure coding to ensure data integrity.
How does Network Attached Storage work?
Simply put, NAS is an approach to making stored data more accessible among devices on a network. By installing specialized software on dedicated hardware, enterprises can benefit from shared, single-point access with built-in security, management, and fault tolerant capabilities. NAS communicates with other devices using file-based protocols, which are 1 of the easiest formats to navigate (compared to block or object storage).
Network Attached Storage hardware may be referred to as a NAS box, NAS unit, NAS server, or NAS head (depending on whom you ask). The server itself is essentially configured with storage disks or drives, processors, and random-access memory (RAM)—much like any other server. A NAS unit may be configured with more RAM, and the drive types and capacity may be similarly configured to meet the needs of specified use. But the main differences between NAS and general-purpose server storage lie in the software.
A NAS box includes software that’s deployed on a stripped-down operating system, usually embedded in the hardware. Compare that to a general-purpose server that uses a full-fledged operating system—sending and receiving hundreds or thousands of small, unique requests every second. By contrast, a NAS operating system takes care of just 2 things: data storage and file sharing.
A NAS box is formatted with data transfer protocols, which are standard ways of sending data between devices. These protocols can be accessed by clients through a network switch, which is a central server that connects to everything and routes requests. Data transfer protocols basically let you access another computer’s files as if they were your own.
Networks can run multiple data transfer protocols, but 2 are fundamental to most networks: the internet protocol (IP) and the transmission control protocol (TCP). TCP combines data into packets before they’re sent through an IP. Think about TCP packets as compressed zip files and IP as email addresses. If your grandparents aren’t on social media and don’t have access to your personal cloud, you have to send them vacation photos via email. Instead of sending those photos 1-by-1, you can bundle them into zip files and send them over a few at a time. In a similar fashion, TCP combines files into packets before they’re sent across a network via IPs.
The files transferred across the protocols can be formatted as:
- Network File Systems (NFS): This protocol is regularly used on Linux and UNIX systems. As a vendor-agnostic protocol, NFS works on any hardware, operating system, or network architecture.
- Server Message Blocks (SMB): Most systems that use SMB run Microsoft Windows, where it’s known as “Microsoft Windows Network.” SMB developed from the common internet file sharing (CIFS) protocol, which is why you might see it referred to as the CIFS/SMB protocol.
- Apple filing protocol (AFP): A proprietary protocol for Apple devices running macOS.
So, is NAS a cloud?
No. NAS by itself is not a cloud. Clouds are pools of virtual resources (yes, like storage) orchestrated by management and automation software so they can be accessed by users on-demand through self-service portals supported by automatic scaling and dynamic resource allocation. NAS would need to be virtualized into resource pools before it could be called a cloud, and those pools would need to be orchestrated by management and automation software before it could be considered cloud computing.
If you put local storage on 1 side of a spectrum and cloud storage on the other, NAS is somewhere in between. NAS has some local storage features (onsite, hardwired connections) and some cloud storage features (self-service, networked access), but doesn’t include the management and automation software necessary to rapidly scale and provide metered service. NAS isn’t a cloud, but it can serve a fundamental role in cloud computing.
Network-attached storage compared to other storage types
Storage Area Networks
A storage area network provides what’s known as block storage. Block storage splits storage volumes—like hard disks, virtualized storage nodes, or pools of cloud-based storage resources—into smaller volumes known as blocks, each of which can be formatted with different protocols. For example, 1 block can be formatted for NFS, another can be formatted for AFP, and a third can be formatted for SMB. This gives users more flexibility, but also means they have to navigate everything manually since block storage bundles data together using arbitrary classifications.
Direct-attached storage is storage that’s directly attached to a single computer. It’s not networked and so can’t easily be accessed by other devices. DAS was the precursor to NAS, and each DAS device must be managed separately (compared to NAS, which manages everything). The most common example of DAS is a single computer’s hard drive. In order for another computer to access files on that drive, it must be physically removed from the original computer and attached to the new one, or a user must set up some sort of connection between the 2 devices.
Software-defined storage (SDS) is storage management software that operates independently of the underlying hardware. That means it’s possible to install SDS on a NAS box, which allows the hardware to be tailored to specific workloads. With SDS installed, storage hardware can be clustered so multiple servers can operate as a single system for a specific purpose. For example, 1 server cluster can be configured to hold user directories and NFS/CIFS folders while another is configured for block storage so it can hold photos and multimedia. Some NAS/SDS solutions can even consolidate and deliver more than a petabyte of data in 30 minutes or less.
AS differs from the traditional file serving and Direct Attached Storage 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. NAS systems usually contain one or more hard disks, often arranged into logical, redundant storage containers or RAIDs (redundant arrays of independant 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 NAS 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 network (SAN) which uses a block-based approach and generally runs over SCSI over Fibre Channel or iSCSI. (There are other SAN protocols as well, such as ATA over Ethernet and HyperSCSI, which however are less common.)
Minimal-functionality or stripped-down operating systems are used on NAS computers or devices which run the protocols and file applications that provide the NAS functionality. A “leaned-out” FreeBSD is used in FreeNAS, for example, which is open source NAS software meant to be deployed on standard computer hardware. Commercial embedded devices and consumer “network appliances” may use closed source operating systems and protocol implementations.
History of Network-Attached Storage
Network-attached storage was introduced with the early file-sharing Novell’s NetWare server operating system and NCP protocol in 1983. In the UNIX world, Sun Microsystems’ 1984 release of NFS allowed network servers to share their storage space with networked clients. 3Com’s 3Server and 3+Share software were the first purpose-built servers (including proprietary hardware, software, and multiple disks) for open systems servers, and the company led the segment from 1985 through the early 1990s. 3Com and Microsoft would develop the LAN Manager software and protocol to further this new market. Inspired by the success of file servers from Novell, IBM, and Sun, several firms developed dedicated file servers. While 3server was among the first firms to build a dedicated NAS for desktop operating systems, Auspex Systems was one of the first to develop a dedicated NFS server for use in the UNIX market. A group of Auspex engineers split away to create the integrated Network Appliance “filer”, which supported both Windows and UNIX, in the early 1990s, starting the market for proprietary NAS arrays.
Benefits to NAS
The Availability of data can potentially be increased with NAS because data access is not dependent on a server: the server can be down and users will still have access to data on the NAS. Performance can be increased by NAS because the file serving is done by the NAS and not done by a server responsible for also doing other processing. The performance of NAS devices, though, depends heavily on the speed of and traffic on the network and on the amount of cache memory (the equivalent of RAM) on the NAS computers or devices. The scalability of NAS is not limited by the number of internal or external ports of a server’s data bus, as a NAS device can be connected to any available network jack. NAS can be more reliable than DAS because it separates the storage from the server. If the server fails, there is unlikely to be file system corruption, although partially-created files may linger. However, if the power source or OS of the NAS fails, corruption is still possible.
Drawbacks to NAS
Due to the multiprotocol, and the reduced CPU and OS layer, the NAS has its limitations compared to the DAS/FC systems. If the NAS is occupied with too many users or too many I/O or CPU processing power that is too demanding, , the NAS reaches its limitations. A server system is easily upgraded by adding one or more servers into a cluster, so CPU power can be upgraded. While the NAS is limited to its own hardware, which is in most cases not upgradable.
NAS is useful for more than just general centralized storage provided to client computers in environments with large amounts of data. NAS can enable simpler and lower cost systems such as load-balancing and fault-tolerant email and web server systems by providing storage services. The potential emerging market for NAS is the consumer market where there is a large amount of multi-media data. Such consumer market appliances are now commonly available. Unlike their rack-mounted counterparts, they are generally packaged in smaller form factors. The price of NAS appliances has plummeted in recent years, offering flexible network-based storage to the home consumer market for little more than the cost of a regular USB or FireWire external hard disk. Many of these home consumer devices are built around ARM, PowerPC or MIPS processors running an embedded Linux operating system. Examples include Buffalo’s TeraStation and Linksys NSLU2.
A NAS head refers to a NAS which does not have any on-board storage but instead connects to a SAN. In effect, it acts as a translator between the file-level NAS protocols (NFS, CIFS,etc.) and the block-level SAN protocols (Fibre Channel, iSCSI). Thus it can combine the advantages of both technologies.