network-attached storage (NAS)

What is network-attached storage (NAS)?

Network-attached storage (NAS) is dedicated file storage that enables multiple users and heterogeneous client devices to retrieve data from centralized disk capacity. Users on a local area network (LAN) access the shared storage via a standard Ethernet connection.

NAS devices typically do not have a keyboard or display and are configured and managed with a browser-based utility. Each NAS resides on the LAN as an independent network node, defined by its own unique Internet Protocol (IP) address.

NAS stands out for its ease of access, high capacity and low cost. The devices consolidate storage in one place and support a cloud tier and tasks, such as archiving and backup.

NAS and storage area networks (SANs) are the two main types of networked storage. NAS handles unstructured data, such as audio, video, websites, text files and Microsoft Office documents. SANs are designed primarily for block storage inside databases, also known as structured data.

What is network-attached storage used for?

The purpose of NAS is to enable users to collaborate and share data more effectively. It is useful to distributed teams that need remote access or work in different time zones. NAS connects to a wireless router, making it easy for distributed workers to access files from any desktop or mobile device with a network connection. Organizations commonly deploy a NAS environment as the foundation for a personal or private cloud.

Some NAS products are designed for use in large enterprises. Others are for home offices or small businesses. Devices usually contain at least two drive bays, although single-bay systems are available for noncritical data. Enterprise NAS gear is designed with more high-end data features to aid storage management and usually comes with at least four drive bays.

Prior to NAS, enterprises had to configure and manage hundreds or even thousands of file servers. To expand storage capacity, NAS appliances are outfitted with more or larger disks, known as scale-up NAS. Appliances are also clustered together for scale-out storage.

In addition, most NAS vendors partner with cloud storage providers to give customers the flexibility of redundant backup.

While collaboration is a virtue of NAS, it can also be problematic. Network-attached storage relies on hard disk drives (HDDs) to serve data. Input/output (I/O) contention can occur when too many users overwhelm the system with requests at the same time. Newer systems use faster flash storage, either as a tier alongside HDDs or in all-flash configurations.

With a NAS system, distributed work environments can easily access files and folders from any network-connected device.

NAS use cases and examples

The applications to be used determine the type of HDD selected for a NAS device. Sharing Microsoft Excel spreadsheets or Word documents with co-workers is a routine task, as is performing periodic data backup. Conversely, using NAS to handle large volumes of streaming media files requires larger capacity disks, more memory and more powerful network processing.

At home, people use a NAS system to store and serve multimedia files and to automate backups. Home users rely on NAS to do the following:

  • manage smart TV storage;
  • manage security systems and security updates;
  • manage consumer-based internet of things components;
  • create a media streaming service;
  • manage torrent files;
  • host a personal cloud server; and
  • create, test and develop a personal website.

In the enterprise, NAS is used:

An example of how enterprises use the technology is when a company imports many images every day. The company cannot stream this data to the cloud because of latency. Instead, it uses an enterprise-class NAS to store the images and cloud caching to maintain connections to the images stored on premises.

Higher-end NAS products have enough disks to support redundant array of independent disks, or RAID, which is a storage configuration that turns multiple hard disks into one logical unit to boost performance, high availability and redundancy.

Network-attached storage devices from Netgear
Netgear is one of several popular NAS vendors.

NAS product categories

NAS devices are grouped in three categories based on the number of drives, drive support, drive capacity and scalability.

High-end or enterprise

The high end of the market is driven by organizations that need to store vast quantities of file data, including virtual machine (VM) images. Enterprise devices provide rapid access and clustering capabilities. The clustering concept addresses drawbacks associated with traditional NAS.

For example, one device allocated to an organization's primary storage space creates a potential single point of failure. Spreading mission-critical applications and file data across multiple boxes and adhering to scheduled backups decrease the risk.

Clustered NAS systems also reduce NAS sprawl. A distributed file system runs concurrently on multiple NAS devices. This approach provides access to all files in the cluster, regardless of the physical node on which it resides.


The midmarket accommodates businesses that require several hundred terabytes (TB) of data. These devices cannot be clustered, however, which can lead to file system siloes if multiple NAS devices are required.

Low-end or desktop

The low end is aimed at home users and small businesses that require local shared storage. This market is shifting toward a cloud services model, with products such as Buurst's SoftNAS Cloud and software-defined storage (SDS) from legacy storage vendors.

NAS categories
Find out about the three basic types of NAS systems: low-end, midmarket and high-end NAS.

NAS deployments for business

The chart below describes five different ways network-attached storage can be deployed and lists the pros and cons for each approach. Each deployment can easily be managed by a single network manager.

The different deployment approaches include:

  • NAS gateways. These are best for large, enterprise-class users who have a SAN.
  • Integrated NAS. This approach works well for users of all sizes without a SAN.
  • Clustered file systems. Large compute cluster users who need high-performance access to file data find these clustered file systems
  • Parallel file systems. These also work well for large compute cluster users requiring high-performance file data access or any organization needing parallel access to file data.
  • NAS aggregators. These are ideal for multibox and multivendor environments.
NAS deployment options
Learn about the pros and cons of various approaches to implementing NAS.

What's the future of network-attached storage?

The baseline functionality of NAS devices has broadened to support virtualization. High-end NAS products may also support data deduplication, flash storage, multiprotocol access and data replication.

Some NAS devices run a standard operating system, such as Microsoft Windows, while others run a vendor's proprietary OS. IP is the most common data transport protocol, but some midmarket NAS products may support additional protocols, such as:

Additionally, high-end NAS devices may support Gigabit Ethernet for even faster data transfer across the network.

Some larger enterprises are switching to object storage for capacity reasons. However, NAS devices are expected to continue to be useful for small and medium-sized businesses.

Scale-up and scale-out NAS vs. object storage

Scale-up and scale-out are two versions of NAS. Object storage is an alternative to NAS for handling unstructured data.

Scale-up NAS

In a network-attached storage deployment, the NAS head is the hardware that performs the control functions. It provides access to back-end storage through an internet connection. This configuration is known as scale-up architecture. A two-controller system expands capacity with the addition of drive shelves, depending on the scalability of the controllers.

Scale-out NAS

With scale-out systems, the storage administrator installs larger heads and more hard disks to boost storage capacity. Scaling out provides the flexibility to adapt to an organization's business needs. Enterprise scale-out systems can store billions of files without the performance tradeoff of doing metadata searches.

Object storage

Some industry experts speculate that object storage will overtake scale-out NAS. However, it's possible the two technologies will continue to function side by side. Both storage methodologies deal with scale, but in different ways.

NAS files are centrally managed via the Portable Operating System Interface (POSIX). It provides data security and ensures multiple applications can share a scale-out device without fear that one application will overwrite a file being accessed by other users.

Object storage is a new method for easily scalable storage in web-scale environments. It is useful for unstructured data that is not easily compressible, particularly large video files.

Object storage does not use POSIX or any file system. Instead, all the objects are presented in a flat address space. Bits of metadata are added to describe each object, enabling quick identification within a flat address namespace.


Direct-attached storage (DAS) refers to a dedicated server or storage device that is not connected to a network. A computer's internal HDD is the simplest example of DAS. To access DAS files, the user must have access to the physical storage.

DAS has better performance than NAS, especially for compute-intensive software programs. In its barest form, DAS may be nothing more than the drives that go in a server.

With DAS, the storage on each device must be separately managed, adding a layer of complexity. Unlike NAS, DAS does not lend itself well to shared storage by multiple users.

NAS vs. SAN vs. DAS
See how SAN, DAS and NAS platforms compare.


What are the differences between SAN and NAS? A SAN organizes storage resources on an independent, high-performance network. Network-attached storage handles I/O requests for individual files, whereas a SAN manages I/O requests for contiguous blocks of data.

Diagram showing NAS vs. SAN storage
See how NAS and SAN compare.

NAS traffic moves across Transmission Control Protocol/Internet Protocol, such as Ethernet. SAN, on the other hand, routes network traffic over the Fibre Channel (FC) protocol designed specifically for storage networks. SANs can also use the Ethernet-based Internet Small Computer System Interface (iSCSI) protocol instead of FC.

While NAS can be a single device, a SAN provides full block-level access to a server's disk volumes. Put another way, a client OS will view NAS as a file system, while a SAN appears to the disk as the client OS.

SAN/NAS convergence

Until recently, technological barriers have kept the file and block storage worlds separate. Each has had its own management domain and its own strengths and weaknesses. The prevailing view of storage managers was that block storage is first class and file storage is economy class. Giving rise to this notion was a prevalence of business-critical databases housed on SANs.

With the emergence of unified storage, vendors sought to improve large-scale file storage with SAN/NAS convergence. This consolidates block- and file-based data on one storage array. Convergence supports SAN block I/O and NAS file I/O in the same set of switches.

The concept of hyper-convergence first appeared in 2014, pioneered by market leaders Nutanix and SimpliVity Corp., now part of Hewlett Packard Enterprise (HPE). Hyper-converged infrastructure (HCI) bundles the computing, network, SDS and virtualization resources on a single appliance.

HCI systems pool tiers of different storage media and present it to a hypervisor as a NAS mount point. They do this even though the underlying shared resource is block-based storage. However, a drawback of HCI is that only the most basic file services are provided. That means a data center may still need to implement a separate network with attached file storage.

Converged infrastructure (CI) packages servers, networking, storage and virtualization resources on hardware that the vendor has prevalidated. Unlike HCI, which consolidates devices in one chassis, CI is separate devices. This gives customers greater flexibility in building their storage architecture. Organizations looking to simplify storage management may opt for CI or HCI systems to replace a NAS or SAN environment.

NAS and file storage vendors

Despite the growth in flash storage, NAS systems still primarily rely on spinning media. The list of vendors is extensive, with most offering more than one configuration to help customers balance capacity and performance.

NAS systems come fully populated with disks or as a diskless chassis where customers add HDDs from their preferred vendor. Drive-makers Seagate Technology, Western Digital and others work with NAS vendors to develop and qualify media.

Vendors of NAS appliances or scalable file storage include the following:

  • Accusys Storage Ltd. supplies scalable shared flash with Peripheral Component Interconnect Express-based ExaSAN. Accusys Gamma and T-Share devices are Thunderbolt 2-designed devices with built-in RAID.
  • Asustor is a subsidiary of Taiwanese computer electronics giant Asus. It offers NAS models for personal and business use.
  • Buffalo Americas Inc. offers TeraStation desktop and rackmount NAS appliances. Buffalo's LinkStation NAS devices are targeted at small business and individuals.
  • Buurst SoftNAS Cloud NAS software-only product enables customers to scale data migration to Amazon Web Services, Microsoft Azure and VMware vSphere.
  • ClearSky Data added a scale-up NAS option as a managed service to complement its block storage and hybrid data protection.
  • DataDirect Networks specializes in storage systems for high-performance computing, including the ExaScaler arrays engineered for high parallelization.
  • DataOn Storage certified its scale-out file server to enable tunable, shared clustered storage to Windows Server 2019.
  • Dell EMC Isilon is a scale-out NAS offered in a disk and an all-flash model.
  • Drobo 5N NAS is a low-end complement to the Drobo B810i and B1200i iSCSI midrange arrays.
  • Excelero Inc. jumped in the market in 2017 with NVMesh Server SAN software, which sits between block drives and logical file systems. It writes data directly to non-volatile memory express devices using its patented Remote Direct Drive Access.
  • Fujitsu Celvin NAS servers are suited for backup, cloud, file sharing and SAN integration cases.
  • Hitachi Vantara offers Hitachi NAS Platform, which combines Hitachi's Virtual Storage Platform arrays and Storage Virtualization Operating System and is geared to large VMware environments.
  • HPE branched into NAS with StoreEasy models in varying capacities and price points.
  • Huawei OceanStor 9000 features a symmetrically distributed architecture that scales from three to 288 nodes.
  • IBM Spectrum NAS combines IBM Spectrum SDS with storage hardware. Spectrum NAS runs on x86 servers. IBM Spectrum Scale handles file storage for high-performance computing. Spectrum Scale is SDS based on IBM's General Parallel File System.
  • Infinidat built the petabyte-scale InfiniBox unified NAS and SAN array predominantly with disk. It used a B-tree architecture that caches data and metadata on SSDs, enabling reads directly on the nodes.
  • IXSystems Inc. designs consumer-oriented FreeNAS and TrueNAS for enterprises. Customers can purchase bundled IXSystems TrueOS software and TrueNAS hardware or download and install FreeOS on their preferred choice of servers.
  • Microsoft Avere Systems FXT Edge Filer, with a file system designed for object storage, offers cloud-integrated hybrid storage that works with an organization's NAS and Azure Blob Storage.
  • NetApp Inc. helped pioneer the use of an extensible file system with its Fabric-Attached Storage and All Flash FAS.
  • Netgear ReadyNAS is available in desktop and rackmount models as storage for hybrid and private clouds.
  • Nexenta NexentaStor is SDS that also supports FC and NAS. The software runs on bare metal, VMware hosts or inside VMs on hyper-converged hardware.
  • Nexsan Unity durability-focused arrays handle SAN and NAS protocols, enabling hybrid media to support mixed workloads, especially in rugged physical locations.
  • Panasas ActiveStor parallel hybrid scale-out system runs the PanFS file system.
  • Pure Storage positions its all-flash FlashBlade as a highly scalable platform for big data analytics.
  • QNAP Systems Inc. has an extensive NAS portfolio that spans small and midsize businesses, as well as midrange and high-end enterprises. It also has products for home users.
  • Quantum Corp. launched Xcellis scale-out NAS to compete with Dell EMC Isilon and NetApp FAS. Xcellis uses the Quantum StorNext scalable file system.
  • Qumulo Inc. Core file storage was developed by several of the creators of the Dell EMC Isilon technology. The Core OS runs on Qumulo C-series and P-series branded arrays, as well as commodity servers.
  • Rackspace enterprise services include dedicated NAS based on the NetApp OnTap OS for managed block- and file-level storage.
  • RackTop Systems integrates BrickStor unified storage with Seagate disk and StorOne enclosures and sells it as the Secure Data Protection Platform.
  • Seagate BlackArmor NAS 220 enterprise arrays scale from 1 TB to 6 TB, with smaller BlackArmor models topping out at 2 TB. Seagate Personal Cloud NAS targets the consumer market with capacity up to 5 TB.
  • Spectra Logic introduced BlackPearl NAS ranging from 48 TB to 420 TB of optional hybrid flash in a 4U rack.
  • StorageCraft Technology Corp. doesn't technically have NAS but positions the OneXafe platform as a scale-out alternative.
  • Synology Inc. offers NAS devices for business and personal uses, including DiskStation NAS, FS/XS Series, J Series, Plus Series and Value Series.
  • Thecus Technology Corp. markets a range of NAS appliances.
  • Verbatim Corp. PowerBay NAS supports four hot-swappable HDD cartridges that can be configured for various RAID levels. Verbatim is a subsidiary of Mitsubishi Chemical Corp.
  • WekaIO VM-deployed NAS software gets installed on flash-enabled x86 servers, using its parallel file system to scale to trillions of files.
  • Western Digital Corp. My Cloud NAS comes in various models with branded HelioSeal helium HDDs. Portable, rugged NAS also is available through Western Digital's G-Technology subsidiary.
  • Zadara Storage cloud NAS provides scalable file storage as a service with the software-defined Zadara VPSA Storage Array.

Cloud-based file storage

In addition to NAS devices, some data centers augment or replace physical NAS with cloud-based file storage. Amazon Elastic File System is the scalable storage in Amazon Elastic Compute Cloud. Similarly, Microsoft Azure File Service furnishes managed file shares based on SMB and CIFS that local and cloud-based deployments can use.

Not as common now, NAS gateways formerly enabled files to access externally attached storage, either connecting to a high-performance area network over FC or just a bunch of disks in attached servers. NAS gateways are still in use, but less frequently; customers are more likely to use a cloud storage gateway, object storage or scale-out NAS.

A cloud gateway sits at the edge of a company's data center network, shuttling applications between local storage and the public cloud. Nasuni Corp. created the cloud-native UniFS file system software, bundled on Dell PowerEdge servers or available as a virtual storage appliance.

Nasuni rival Panzura provides a similar service with its Panzura CloudFS file system and Freedom Filer cache appliances.

Learn more about five key benefits of cloud storage: scalability, flexibility, multi-tenancy, simpler data migration and lower cost disaster recovery.

This was last updated in August 2021

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