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What is network-attached storage (NAS)? A complete guide

By Stephen J. Bigelow

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 don't 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 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.

Network-attached storage 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, as well as block storage for enterprise applications.

What is network-attached storage used for?

The purpose of network-attached storage 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 a storage filer or 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; this is 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.

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

NAS use cases and examples

The type of HDD selected for a NAS device will depend on the applications to be used. 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 network-attached storage to do the following:

In the enterprise, NAS is used in the following ways:

Take this example of how enterprises use the technology: When a company imports many images every day, it 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 arrays 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. 

NAS components and how they work

A NAS device is fundamentally a dedicated storage server -- a specialized computer designed and intended to support storage through network access. Regardless of the size and scale of the network-attached storage, every NAS device is typically composed of four major components:

Top considerations for choosing NAS

Although the storage goals of NAS might seem straightforward, selecting a NAS device can be deceptively complex. Price considerations aside, enterprise NAS users should consider an array of factors in product selection, including the following:

Why is choosing the right NAS important?

Any network-attached storage deployment is an investment of capital and time, and the storage offered by NAS will be a valuable resource for users -- whether at home, within a small business or across an enterprise. Consequently, a NAS investment demands careful evaluation of each consideration above before making a purchase decision. Choosing the wrong network-attached storage can result in undesirable outcomes, such as the following:

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 and share vast quantities of file data, including virtual machine (VM) images. Enterprise NAS devices can scale to provide petabytes of storage, serve thousands of client systems and 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 decreases the risk. Redundancy is typically accomplished through some form of duplication -- copying data onto more than one storage device or storage subsystem.

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.

Midmarket

The NAS midmarket accommodates businesses with hundreds of client systems that require several hundred terabytes of data. These devices cannot be clustered, however, which can lead to file system silos if multiple NAS devices are required.

Low end or desktop

The NAS low end is aimed at home users and small businesses that require local shared storage for just a few client systems up to several terabytes. This market is shifting toward a cloud NAS service model, with products such as Buurst's SoftNAS Cloud NAS and software-defined storage (SDS) from legacy storage vendors.

NAS deployments for business

The chart below describes five different ways NAS 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 these options:

NAS file-sharing protocols

The baseline functionality of network-attached storage devices has broadened to support virtualization. High-end NAS products might 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 might support additional protocols, such as the following:

Additionally, high-end NAS devices might 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 scale-out and object 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.

NAS vs. DAS

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 or computer must have access to the physical storage.

DAS has better performance than NAS, especially for compute-intensive software programs. This is due to dedicated disk access while avoiding the latency of network traffic. In its barest form, DAS might 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

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.

NAS traffic moves across TCP/IP, 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 iSCSI protocol instead of FC.

Although NAS can be a single device, 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.

But the promise of SAN/NAS convergence goes far beyond a simple matter of storage approach. Designers have long recognized that SAN and NAS are complementary rather than competing storage technologies, and combining SAN and NAS into a single storage system can benefit users in a range of way, including the following:

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 might 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 already integrated and validated. Unlike HCI, which consolidates devices in one chassis, CI employs separate devices. This gives customers greater flexibility in building their storage architecture. Organizations looking to simplify storage management might opt for CI or HCI systems to replace a NAS or SAN environment.

Today's convergence and HCI offerings not only combine SAN and NAS storage, but also consolidate computing (servers) and networking gear into the same gear suite -- optimizing entire data center deployment and build-out opportunities.

NAS and file storage vendors

Despite the growth in flash storage, network-attached storage 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 either fully populated with disks or as a diskless chassis where customers add HDDs from their preferred vendor. Drive vendors Seagate Technology, Western Digital and others work with NAS providers to develop and qualify media.

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

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's Azure Files service furnishes managed file shares based on SMB and CIFS that local and cloud-based deployments can use.

Ideally, cloud-based file storage enables a user or business to store and access data from cloud storage with the same ease and convenience as a local NAS device in the data center or desktop. Cloud file storage has many varied use cases, including web serving, content management, data analytics, data backups and archiving, streaming content and software development. Simultaneously, the cloud provider must support key storage attributes including high availability, good performance, high security, comprehensive management and modest cost. The following are some common cloud file storage options:

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 simply 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.

What's the future of network-attached storage?

Two central themes for future NAS development include diversification and automation.

Diversification. Although the concepts of SAN/NAS convergence offer a compelling glimpse into one possible storage future, businesses can be leery of one-size-fits-all platforms. NAS use cases are diversifying, and the needs of each specific use case must be carefully evaluated. Some NAS offerings are well suited for backups and archives but might not possess the performance, scale and reliability attributes needed for hosting virtualized environments, data analytics, AI/ML computing and demanding databases. As the variety of NAS products grows, it's important for IT and business leaders to select the NAS platform that best meets the needs of the task at hand.

Automation. The diversification of NAS and file storage also carries enormous management challenges to data integrity and data quality. Data has to be on the right platform -- or in the proper pool -- such as NVMe-based NAS for top performance, disk-based NAS for capacity or cloud NAS for convenience. This need is driving the use of automation to put the right data in the right NAS locations and ensure that all of the data is complete, intact and secure -- while reducing the need for human intervention.

Still, NAS is expected to coexist with SAN and object storage subsystems well into the future to meet a wide array of technical and business needs.

30 Sep 2022

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