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Network-attached storage (NAS) is a type of dedicated file storage device that provides local-area network (LAN) users with centralized, consolidated disk storage through a standard Ethernet connection.
Each NAS device is connected to the LAN as an independent network device and assigned an IP address. The primary advantage is that network storage is not limited to the storage capacity of a computing device or the number of disks in a local server. Many NAS products can hold enough disks to support RAID, and multiple NAS appliances can be attached to the network for storage expansion.
NAS devices typically do not have a keyboard or display and are configured through a Web-based management utility. Some NAS boxes run a standard operating system (OS) such as Microsoft Windows, while others may run their own proprietary OSes. Although the Internet Protocol (IP) is the most common network protocol, some NAS products may support other network protocols such as Network File System (NFS), Internetwork Packet Exchange (IPX), NetBIOS Extended User Interface (NetBEUI) or Common Internet File System (CIFS), an enhanced version of the Microsoft open, cross-platform Server Message Block (SMB) protocol. Some NAS products also support Gigabit Ethernet (GigE) for faster data transfers across the network.
Development and evolution of NAS
NAS evolved as a low-cost, turnkey storage alternative to block-based storage-area networks (SANs). Adoption of the technology can be traced to the small and medium-sized business (SMB) market during the early 2000s, due to its ability to provide reliable and fast file serving across multiple platforms. Over time, baseline functionality of NAS has improved to include features that support virtualization, high availability and data redundancy.
NAS pros and cons
Largely due to its ease of deployment with multiple file systems, NAS remains a popular storage option with SMBs. In addition, NAS array vendors are incorporating a broader range of features such as data deduplication, support for flash drives, multiprotocol access, NAS gateways and replication.
The benefits of NAS include fast file access for multiple clients, ease of data sharing and drive mirroring, expandable storage capacity, data redundancy and flexible consolidation of resources. The biggest drawback of NAS is an inability to conveniently move large blocks of data.
The chart below describes the five basic approaches to deploying NAS. They include NAS gateways for large enterprises, integrated NAS for SMBs, clustered NAS and parallel file systems for large computing environments, and NAS aggregators for heterogeneous storage.
NAS product categories
NAS devices are grouped in three broad categories based on the number of drives, drive support, drive capacity and scalability.
High-end or enterprise NAS: This is the high end of the market, driven by the need to store huge amounts of files, including virtual machine (VM) images, as well as the need for rapid access and NAS clustering.
Midmarket NAS: This end of the market can run to capacities of several hundred terabytes. Midmarket NAS devices cannot be clustered, which leads to file-system siloes if multiple NAS devices are required.
NAS vs. DAS
Network-attached storage can make it easier to promote file sharing and scale high-performance storage than direct-attached storage (DAS), which is non-networked storage that connects to a dedicated server or computer hard drive. Multiple NAS boxes can be attached to a network to expand storage capacity. NAS systems also provide a single view of available storage to LAN users. Conversely, DAS requires that the storage for each server be managed separately, complicating data transfer in a networked environment, although DAS may provide higher performance than NAS for accelerating certain applications.
NAS vs. SAN
The key distinction between NAS and SANs is that NAS handles file-based I/O requests, whereas a SAN manages block I/O requests. SANs can be Ethernet-based, but usually run on a Fibre Channel protocol developed specifically for storage networks. NAS provides file-level access to storage by using a remote protocol to direct I/O access requests to storage. This enables file sharing and the ability to centralize data management. From a server application and OS perspective, NAS behaves similarly to a SAN in how it accesses data.
Traditional NAS vs. scale-out NAS
In a traditional deployment, a NAS head provides access to back-end storage via an Internet connection to access, manage and store files. Expanding NAS connectivity requires users to install larger heads and additional hard disks to boost storage capacity. Clustered NAS systems have emerged to tame NAS sprawl by aggregating a large number of front-end NAS nodes and back-end storage pools that can scale to the petabyte range.
NAS use cases
Increased file storage capacity is fueling the purchase of NAS systems. Prior to network-attached systems, enterprises typically had hundreds or even thousands of discrete file servers that had to be separately configured and maintained. Most NAS appliances can be outfitted with larger disks to boost storage capacity. NAS arrays often are used as backup targets for archiving, disaster recovery and redundant storage. Other use cases include consolidating large numbers of discrete file servers, reduced licensing and maintenance costs, technology refreshes and increased flexibility.
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