Network-attached storage (NAS) is a storage device or system connected to a local network that stores files and shares them with users, servers and applications over standard file-sharing protocols. To the people using it, a NAS appears as shared drives or folders. It ranges from a small appliance with a few disks in a branch office to clustered enterprise systems holding very large amounts of data, and the same idea is now also sold as a managed cloud file service.
At a glance
- Works at the file level: users and applications open folders and files by name, not raw disks.
- Connects over the ordinary Ethernet network and uses common file protocols, such as SMB for Windows and NFS for Linux and Unix.
- Usually an appliance with its own operating system, disks in a redundant configuration and a management interface.
- Commonly used for shared department drives, home folders, media and design files, scanned documents and backup targets.
- Available on premises, as clustered scale-out systems, and as cloud or hybrid file services.
What problem it solves
Without central storage, files end up on individual PCs, old servers and personal cloud accounts. Nobody knows which copy is current, storage is full in one place and empty in another, and a single failed laptop or server can take important data with it. Running a general-purpose server just to share files also means another operating system to patch and license.
A NAS gives an office or organization one dedicated place to store and share files, with permissions tied to user accounts, redundancy against individual drive failures, and room to grow by adding disks or nodes. It is simple to deploy compared with a storage area network (SAN), and many models include snapshots, replication and remote access.
How it works
Hardware. A NAS contains disks, a processor, memory and network ports. Disks are grouped in a RAID or similar arrangement so the system keeps working if a drive fails, though rebuilding a failed drive can take hours or days and slows performance while it runs.
File system and protocols. The NAS formats its disks with its own file system and shares folders over the network using file protocols: SMB is standard for Windows clients, NFS for Linux and Unix servers and many virtualization platforms. Users and servers mount these shares as network drives. Permissions usually tie into the organization’s directory, so access follows user accounts.
Scale. Small NAS appliances grow by adding or replacing disks until the chassis is full. Scale-out NAS clusters grow by adding nodes, presenting one large file system across all of them, which suits very large data sets such as video, research or imaging.
Data protection features. Many systems take snapshots, point-in-time copies that let users restore earlier versions of files, and replicate data to a second NAS or to the cloud. Some offer immutable snapshots that cannot be changed or deleted for a set period, a useful defense against ransomware.
Performance. NAS performance depends on disk type, caching, network speed and how many users or applications hit it at once. It is commonly measured in throughput and input/output operations per second (IOPS). Flash-based NAS can support demanding workloads; disk-based NAS suits bulk file storage.
Our file and object storage page covers how buyers compare file storage options across on-premises and cloud.
When it matters for buyers
- Replacing an aging file server. A NAS or a cloud file service is the usual replacement; decide based on file sizes, bandwidth and how users work.
- Opening or consolidating sites. Branches that work with large files or poor internet may need local storage, ideally synchronized centrally.
- Ransomware readiness. Shared drives are a prime ransomware target. Snapshots, immutable copies and an offsite backup following the 3-2-1 backup rule limit the damage.
- Hardware and support renewals. End of vendor software updates is a security risk as much as an operational one.
- Evaluating hyperconverged or cloud storage. Some hyperconverged and storage as a service offerings include file services that can replace a separate NAS.
Questions to ask vendors
- What usable capacity do we get after redundancy, snapshots and overhead, and how do we expand it?
- Which file protocols and versions are supported, and how does it integrate with our directory?
- What performance can we expect for our workload, and is that based on flash, disk or a mix?
- What snapshot, replication and immutability options are included, and which cost extra?
- How long will this model receive software and security updates?
- How long does a drive rebuild take, and what happens to performance during it?
- What does support include: next-business-day parts, onsite replacement or remote help only?
How it differs from a SAN
A NAS and a SAN both provide shared storage, but at different levels. A NAS manages its own file system and shares files and folders over the regular network, so many users and servers can open the same files. A SAN presents raw storage volumes to servers at the block level, and each server formats and manages its volume as if it were a local disk, typically over a dedicated storage network. NAS is usually simpler and suits shared files; SAN is the traditional choice for databases and virtual machine storage that need consistent low latency. Some storage systems, often called unified storage, provide both from the same hardware.