SAN vs. NAS: what's the practical difference
Quick answer
A SAN presents storage at block level, raw volumes that look like local disks to the server, so the server's own operating system formats and manages the filesystem. A NAS shares storage at file level instead, so multiple clients can read and write the same files and folders at once, with the NAS itself managing the filesystem. Pick a SAN when one server needs direct, high-performance access to its own volume. Pick a NAS when several servers or users need to share the same files.
Two different layers of storage
SAN and NAS both put storage on a network rather than inside the server chassis, but they hand that storage over at different layers, and that's the whole distinction.
A Storage Area Network (SAN) presents raw block volumes over a network protocol, typically iSCSI or Fibre Channel. From the server's point of view, a SAN volume looks exactly like a local disk: it shows up unformatted, and the server's own operating system partitions it, puts a filesystem on it, and manages it from there, the same way it would manage an internal drive. The SAN itself has no idea what files live on the volume. It just serves blocks.
Network Attached Storage (NAS) works a level higher. It shares storage at file level, over protocols such as NFS or SMB, and the NAS device or platform manages the filesystem itself. Clients connect to a share and see folders and files directly, not a raw disk to format. Because the NAS owns the filesystem, multiple clients can connect to the same share at once and see each other's changes, something a single SAN volume generally can't offer without extra clustering software on top.
Why the difference matters in practice
The practical consequences follow directly from that layering.
A block volume mounted from a SAN behaves like a disk that belongs to one server. That server gets direct, low-level access to it, which is exactly what workloads like databases want: consistent, predictable performance without a shared filesystem's overhead sitting in the way. Two servers attaching the same SAN volume at once, without cluster-aware software to coordinate them, usually corrupts data rather than sharing it safely, so a SAN volume is normally treated as belonging to one server at a time.
A NAS share, by contrast, is built for exactly the situation a SAN volume struggles with: several servers, or several people, needing the same files. Team file shares, content that multiple application servers all need to read, and collaborative workflows are the natural fit, because the NAS's own filesystem management is what makes concurrent access safe. The trade-off is that a shared filesystem layer, and the network file protocol on top of it, adds overhead that a raw block volume doesn't carry, so a NAS typically won't match a SAN volume's peak, low-level performance for a single demanding workload.
A practical rule of thumb
| Situation | Better fit | Why |
|---|---|---|
| Database or another high-performance workload owned by one server | SAN | Direct, low-level block access with no shared filesystem overhead |
| Files that multiple servers or users need to access at the same time | NAS | The NAS manages the filesystem, so concurrent access is safe by design |
| Virtual machine disks | SAN | Each VM disk is typically a block volume owned by one host at a time |
| Team shares, shared content directories, collaborative folders | NAS | File-level sharing across many clients is the whole point of NAS |
If you're still unsure which one fits, ask who or what needs to open the data at the same time. One server, on its own volume: SAN. Multiple servers or people, the same files: NAS.