Glossary
Network-attached storage (NAS)
Network-attached storage (NAS) is a system that owns a file system and shares it over an ordinary network, so many users and servers can open the same folders at once. Clients mount a share as a drive, and the NAS enforces permissions and file locking for everyone who connects.
What the NAS takes care of
A NAS holds the folder tree, the file names and the access rules. Linux and Unix hosts usually connect over NFS and Windows clients over SMB, and a directory service decides who may open what. Locking is what makes shared work safe: when two people open the same project file, the NAS stops one from silently overwriting the other. That sets it apart from block storage, which hands out raw volumes and knows nothing about files, and from object storage, which has keys and metadata but no folders to open.
Scale-up and scale-out filers
| Design | How it grows | Where it stops | What happens next |
|---|---|---|---|
| Scale-up filer | Drive shelves added behind one or two controllers | When the controllers run out of processing, memory or ports | A second filer with its own separate folder tree |
| Scale-out NAS | Servers added to a cluster behind one namespace | At the limits of the cluster network and metadata design | More servers, same namespace |
The scale-out design follows the general pattern of scale-out storage: performance rises with capacity, at the price of a more complex system to run.
Why do large NAS estates stall before the disks fill?
At hundreds of terabytes and beyond, the strain usually comes from file count rather than capacity. Hundreds of millions of small files load the metadata that tracks them, so directory listings and searches slow down. Backup jobs have to scan every entry to find what changed, and the backup window stretches long before the drives are full. Each extra scale-up filer adds another namespace, and users start needing to know which filer holds which project. Estates that reach this point are describing storage sprawl, and the usual response is NAS consolidation or moving cold files off the filers.
What stays on file storage
Shared editing, home directories, and applications that expect file locking or rewrite parts of files in place remain NAS work. Large collections that are written once and rarely touched again often move to object storage, sometimes leaving a stub in the folder so the path still works for users and scripts that expect it. How the two compare by access pattern is covered in object storage vs NAS.
Frequently asked questions
What is the difference between NAS and SAN?
A SAN delivers raw block volumes that each server formats with its own file system. A NAS delivers finished, shareable files and keeps the file system itself.
Is a NAS the same as a file server?
Nearly. A NAS is a file server packaged as a dedicated appliance or software system, with an operating system tuned for sharing files.