Network-attached storage (NAS) is a file-level (as opposed to block-level storage) computer data storage server connected to a computer network providing data access to a heterogeneous group of clients. NAS is specialized for serving files either by its hardware, software, or configuration. It is often manufactured as a computer appliance – a purpose-built specialized computer. NAS systems are networked appliances that contain one or more storage drives, often arranged into logical, redundant storage containers or RAID. Network-attached storage removes the responsibility of file serving from other servers on the network. They typically provide access to files using network file sharing protocols such as NFS, SMB, or AFP. From the mid-1990s, NAS devices began gaining popularity as a convenient method of sharing files among multiple computers. Potential benefits of dedicated network-attached storage, compared to general-purpose servers also serving files, include faster data access, easier administration, and simple configuration.
The hard disk drives with "NAS" in their name are functionally similar to other drives but may have different firmware, vibration tolerance, or power dissipation to make them more suitable for use in RAID arrays, which are often used in NAS implementations.For example, some NAS versions of drives support a command extension to allow extended error recovery to be disabled. In a non-RAID application, it may be important for a disk drive to go to great lengths to successfully read a problematic storage block, even if it takes several seconds. In an appropriately configured RAID array, a single bad block on a single drive can be recovered completely via the redundancy encoded across the RAID set. If a drive spends several seconds executing extensive retries it might cause the RAID controller to flag the drive as "down" whereas if it simply replied promptly that the block of data had a checksum error, the RAID controller would use the redundant data on the other drives to correct the error and continue without any problem. Such a "NAS" SATA hard disk drive can be used as an internal PC hard drive, without any problems or adjustments needed, as it simply supports additional options and may possibly be built to a higher quality standard (particularly if accompanied by a higher quoted MTBF figure and higher price) than a regular consumer drive.
A NAS unit is a computer connected to a network that provides only file-based data storage services to other devices on the network. Although it may technically be possible to run other software on a NAS unit, it is usually not designed to be a general-purpose server. For example, NAS units usually do not have a keyboard or display, and are controlled and configured over the network, often using a browser.
A full-featured operating system is not needed on a NAS device, so often a stripped-down operating system is used. For example, FreeNAS or NAS4Free, both open source NAS solutions designed for commodity PC hardware, are implemented as a stripped-down version of FreeBSD.
NAS systems contain one or more hard disk drives, often arranged into logical, redundant storage containers or RAID.
NAS uses file-based protocols such as NFS (popular on UNIX systems), SMB (Server Message Block) (used with MS Windows systems), AFP (used with Apple Macintosh computers), or NCP (used with OES and Novell NetWare). NAS units rarely limit clients to a single protocol.
The key difference between direct-attached storage (DAS) and NAS is that DAS is simply an extension to an existing server and is not necessarily networked. As the name suggests, DAS typically is connected via a USB or Thunderbolt enabled cable. NAS is designed as an easy and self-contained solution for sharing files over the network.
Both DAS and NAS can potentially increase availability of data by using RAID or clustering.
When both are served over the network, NAS could have better performance than DAS, because the NAS device can be tuned precisely for file serving which is less likely to happen on a server responsible for other processing. Both NAS and DAS can have various amount of cache memory, which greatly affects performance. When comparing use of NAS with use of local (non-networked) DAS, the performance of NAS depends mainly on the speed of and congestion on the network. With the introduction of new WiFi standards (like WiFi6), networking speeds and dramatically increase to allow better performance when using a NAS.
NAS is generally not as customizable in terms of hardware (CPU, memory, storage components) or low level software (extensions, plug-ins, additional protocols) but most NAS solutions will include the option to install a wide array of software applications to allow for better configuration of the system or to include other capabilities outside of storage (like video surveillance, virtualization, media, etc). DAS typically is focused solely on data storage but capabilities can be available based on specific vendor options.
NAS provides both storage and a file system. This is often contrasted with SAN (storage area network), which provides only block-based storage and leaves file system concerns on the "client" side. SAN protocols include Fibre Channel, iSCSI, ATA over Ethernet (AoE) and HyperSCSI.
One way to loosely conceptualize the difference between a NAS and a SAN is that NAS appears to the client OS (operating system) as a file server (the client can map network drives to shares on that server) whereas a disk available through a SAN still appears to the client OS as a disk, visible in disk and volume management utilities (along with client's local disks), and available to be formatted with a file system and mounted.
Despite their differences, SAN and NAS are not mutually exclusive and may be combined as a SAN-NAS hybrid, offering both file-level protocols (NAS) and block-level protocols (SAN) from the same system. An example of this is Openfiler, a free software product running on Linux-based systems. A shared disk file system can also be run on top of a SAN to provide filesystem services.
In the early 1980s, the "Newcastle Connection" by Brian Randell and his colleagues at Newcastle University demonstrated and developed remote file access across a set of UNIX machines.Novell's NetWare server operating system and NCP protocol was released in 1983. Following the Newcastle Connection, Sun Microsystems' 1984 release of NFS allowed network servers to share their storage space with networked clients. 3Com and Microsoft would develop the LAN Manager software and protocol to further this new market. 3Com's 3Server and 3+Share software was the first purpose-built server (including proprietary hardware, software, and multiple disks) for open systems servers.
Inspired by the success of file servers from Novell, IBM, and Sun, several firms developed dedicated file servers. While 3Com 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 in the early 1990s to create the integrated NetApp filer, which supported both the Windows SMB and the UNIX NFS protocols and had superior scalability and ease of deployment. This started the market for proprietary NAS devices now led by NetApp and EMC Celerra.
Starting in the early 2000s, a series of startups emerged offering alternative solutions to single filer solutions in the form of clustered NAS – Spinnaker Networks (acquired by NetApp in February 2004), Exanet (acquired by Dell in February 2010), Gluster (acquired by RedHat in 2011), ONStor (acquired by LSI in 2009), IBRIX (acquired by HP), Isilon (acquired by EMC – November 2010), PolyServe (acquired by HP in 2007), and Panasas, to name a few.
In 2009, NAS vendors (notably CTERA Networksand Netgear) began to introduce online backup solutions integrated in their NAS appliances, for online disaster recovery.
By 2021, three major types of NAS solutions are offered (all with hybrid cloud models where data can be stored both on-premise on the NAS and off site on a separate NAS or through a public cloud service provider). The first type of NAS is focused on consumer needs with lower-cost options that typically support 1–5 hot plug hard drives. The second is focused on small-to-medium-sized businesses – these NAS solutions range from 2–24+ hard drives and are typically offered in tower or rackmount form factors. Pricing can vary greatly depending on the processor, components, and overall features supported. The last type is geared toward enterprises or large businesses and are offered with more advanced software capabilities. NAS solutions are typically sold without hard drives installed to allow the buyer (or IT departments) to select the hard drive cost, size, and quality.
The way manufacturers make NAS devices can be classified into three types:
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 rackmounted counterparts, they are generally packaged in smaller form factors. The price of NAS appliances has fallen sharply 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, x86 or MIPS processors running an embedded Linux operating system.
Open-source NAS-oriented distributions of Linux and FreeBSD are available. These are designed to be easy to set up on commodity PC hardware, and are typically configured using a web browser.
They can run from a virtual machine, Live CD, bootable USB flash drive (Live USB), or from one of the mounted hard drives. They run Samba (an SMB daemon), NFS daemon, and FTP daemons which are freely available for those operating systems.
Network-Attached Secure Disks (NASD) is 1997–2001 research project of Carnegie Mellon University, with the goal of providing cost-effective scalable storage bandwidth. NASD reduces the overhead on the file server (file manager) by allowing storage devices to transfer data directly to clients. Most of the file manager's work is offloaded to the storage disk without integrating the file system policy into the disk. Most client operations like Read/Write go directly to the disks; less frequent operations like authentication go to the file manager. Disks transfer variable-length objects instead of fixed-size blocks to clients. The File Manager provides a time-limited cachable capability for clients to access the storage objects. A file access from the client to the disks has the following sequence:
A clustered NAS is a NAS that is using a distributed file system running simultaneously on multiple servers. The key difference between a clustered and traditional NAS is the ability to distribute[ citation needed ] (e.g. stripe) data and metadata across the cluster nodes or storage devices. Clustered NAS, like a traditional one, still provides unified access to the files from any of the cluster nodes, unrelated to the actual location of the data.
The term server highlights the role of the machine in the traditional client–server scheme, where the clients are the workstations using the storage. A file server does not normally perform computational tasks or run programs on behalf of its client workstations.
In computing, iSCSI is an acronym for Internet Small Computer Systems Interface, an Internet Protocol (IP)-based storage networking standard for linking data storage facilities. It provides block-level access to storage devices by carrying SCSI commands over a TCP/IP network. iSCSI is used to facilitate data transfers over intranets and to manage storage over long distances. It can be used to transmit data over local area networks (LANs), wide area networks (WANs), or the Internet and can enable location-independent data storage and retrieval.
A disk enclosure is a specialized casing designed to hold and power disk drives while providing a mechanism to allow them to communicate to one or more separate computers.
A diskless node is a workstation or personal computer without disk drives, which employs network booting to load its operating system from a server.
Direct-attached storage (DAS) is digital storage directly attached to the computer accessing it, as opposed to storage accessed over a computer network. Examples of DAS include hard drives, solid-state drives, optical disc drives, and storage on external drives. The name "DAS" is a retronym to contrast with storage area network (SAN) and network-attached storage (NAS).
A NetApp FAS is a computer storage product by NetApp running the ONTAP operating system; the terms ONTAP, AFF, ASA, FAS are often used as synonyms. "Filer" is also used as a synonym although this is not an official name. There are three types of FAS systems: Hybrid, All-Flash, and All SAN Array:
The NSLU2 is a network-attached storage (NAS) device made by Linksys introduced in 2004 and discontinued in 2008. It makes USB flash memory and hard disks accessible over a network using the SMB protocol. It was superseded mainly by the NAS200 and in another sense by the WRT600N and WRT300N/350N which both combine a Wi-Fi router with a storage link.
TrueNAS is the branding for a range of free and open-source network-attached storage (NAS) operating systems produced by iXsystems, and based on FreeBSD and Linux, using the OpenZFS file system. It is licensed under the terms of the BSD License and runs on commodity x86-64 hardware.
In computing, a shared resource, or network share, is a computer resource made available from one host to other hosts on a computer network. It is a device or piece of information on a computer that can be remotely accessed from another computer transparently as if it were a resource in the local machine. Network sharing is made possible by inter-process communication over the network.
Synology Inc. is a Taiwanese corporation that specializes in Network-attached storage (NAS) appliances. Synology’s line of NAS is known as the DiskStation for desktop models, FlashStation for all-flash models, and RackStation for rack-mount models. Synology's products are distributed worldwide and localized in several languages. Synology's headquarters are located in Taipei, Taiwan, with subsidiaries located around the world.
Isilon is a scale out network-attached storage platform offered by Dell EMC for high-volume storage, backup and archiving of unstructured data. It provides a cluster-based storage array based on industry standard hardware, and is scalable to 50 petabytes in a single filesystem using its FreeBSD-derived OneFS file system.
A clustered file system is a file system which is shared by being simultaneously mounted on multiple servers. There are several approaches to clustering, most of which do not employ a clustered file system. Clustered file systems can provide features like location-independent addressing and redundancy which improve reliability or reduce the complexity of the other parts of the cluster. Parallel file systems are a type of clustered file system that spread data across multiple storage nodes, usually for redundancy or performance.
Panasas is a data storage company that creates network-attached storage for technical computing environments.
Scale out File Services (SoFS) is a highly scalable, grid-based NAS implementation developed by IBM. It is based on IBM's high-performance shared-disk clustered file system Spectrum Scale. SoFS exports the clustered file system through industry standard protocols like SMB, NFS, FTP and HTTP. Released in 2007, SoFS is a second generation file services architecture used within IBM since 2001.
A storage area network (SAN) or storage network is a computer network which provides access to consolidated, block-level data storage. SANs are primarily used to access data storage devices, such as disk arrays and tape libraries from servers so that the devices appear to the operating system as direct-attached storage. A SAN typically is a dedicated network of storage devices not accessible through the local area network (LAN).
Celerra is a discontinued NAS device produced by EMC Corporation until 2011, available either as an integrated unit or as a NAS header which can be added to an independent EMC storage array such as a Clariion or a Symmetrix. It supports the SMB, NFS, FTP, NDMP, TFTP and MPFS protocols. A Celerra Unified Storage device use Clariion storage array as its storage layer and also provides iSCSI and Fibre Channel block-level storage.
OpenMediaVault (OMV) is a free Linux distribution designed for network-attached storage (NAS). The project's lead developer is Volker Theile, who instituted it in 2009. OMV is based on the Debian operating system, and is licensed through the GNU General Public License v3.
Software-defined storage (SDS) is a marketing term for computer data storage software for policy-based provisioning and management of data storage independent of the underlying hardware. Software-defined storage typically includes a form of storage virtualization to separate the storage hardware from the software that manages it. The software enabling a software-defined storage environment may also provide policy management for features such as data deduplication, replication, thin provisioning, snapshots and backup.
XigmaNAS® is a network-attached storage (NAS) server software with a dedicated management web interface. It is free software under the terms of the Simplified BSD license.
ONTAP or Data ONTAP or Clustered Data ONTAP (cDOT) or Data ONTAP 7-Mode is NetApp's proprietary operating system used in storage disk arrays such as NetApp FAS and AFF, ONTAP Select and Cloud Volumes ONTAP. With the release of version 9.0, NetApp decided to simplify the Data ONTAP name and removed word "Data" from it and remove 7-Mode image, therefore, ONTAP 9 is successor from Clustered Data ONTAP 8.
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