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.

What most characterizes NAS is ease of access, high capacity and fairly low cost. NAS devices provide infrastructure to consolidate storage in one place and to support tasks, such as archiving and backup, and a cloud tier.

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 network-attached storage is used for

NAS enables users to collaborate and share data more effectively, particularly work teams that are remotely located or in different time zones. A NAS connects to a wireless router, making it easy for distributed work environments to access files and folders from any device connected to the network. Organizations commonly deploy a NAS environment as the foundation for a personal or private cloud.

There are NAS products designed for use in large enterprises, as well as those 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 discrete file servers. To expand storage capacity, NAS appliances are outfitted with more or larger disks -- known as scale-up NAS -- or 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 NAS systems use faster flash storage, either as a tier alongside HDDs or in all-flash configurations.

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 hard drive is the simplest example of DAS. To access files on direct-attached storage, the end user must have access to the physical storage.

DAS has better performance than NAS, especially for compute-intensive software programs. In its barest form, direct-attached storage may involve nothing more than purchasing the drives to be inserted in a server.

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

NAS vs. SAN

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.

While NAS traffic moves across Transmission Control Protocol/Internet Protocol (TCP/IP), such as Ethernet, a SAN can route network traffic over the FC protocol designed specifically for storage networks. SANs can also use the Ethernet-based iSCSI protocol instead of FC.

While a 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 a NAS as a file system, while a SAN is presented to disk as the client OS.

SAN/NAS Convergence

Until recently, technological barriers have kept the file and block storage worlds separate, each in its own management domain and each with 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 within 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 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, 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, meaning 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 sets of hardware prevalidated by the CI vendor. Unlike HCI, which consolidates devices in one chassis, CI consists of separate devices. This gives customers greater flexibility in building their storage architecture. Organizations looking to simplify storage management may opt for CI and HCI systems to replace a NAS or SAN environment.