Server storage: DAS, NAS and SAN compared
In short: DAS connects disks straight to one server, NAS shares files over the normal network, and a SAN gives servers block-level access to central storage over a dedicated fabric. Block storage suits databases and virtual machines; file storage suits shared folders. Choose by workload, sharing needs and budget.
Block versus file
Before comparing products, understand the two ways a server can see storage. With block storage, the server receives what looks like a blank disk and puts its own file system on it (NTFS, ext4, XFS, VMFS). With file storage, another device owns the file system and the server asks for whole files and folders over the network. A third model, object storage, stores data as objects in buckets accessed by an API, as in cloud services; see cloud storage types.
DAS: direct-attached storage
DAS is storage connected straight to one server: internal drives or an external shelf on a SAS cable. It is fast, simple and cheap. The limit is sharing: only that server can use the disks, and if it fails the data is stuck inside it. DAS is ideal for a single application server, boot drives, and nodes in hyperconverged clusters where software replicates data between servers.
NAS: network-attached storage
A NAS is a device or server that shares files over the ordinary IP network using SMB (common with Windows) or NFS (common with Linux and VMware). Many users and servers can open the same files at once, with permissions controlled by the NAS. It is easy to set up and great for home folders, team shares and backup targets. Performance depends on the LAN, so busy NAS traffic should have its own VLAN or links.
SAN: storage area network
A SAN is a dedicated network that gives servers block access to a shared storage array. The array carves its capacity into LUNs (logical unit numbers), each presented to specific servers. Common transports are:
- Fibre Channel (FC): a separate, lossless fabric with its own switches and host bus adapters (HBAs). Very reliable and low latency, but costly and specialised.
- iSCSI: SCSI commands carried over TCP/IP on standard Ethernet. Cheaper and familiar, best on a separate VLAN or physical network with jumbo frames.
- NVMe over Fabrics (NVMe-oF): newer, very low-latency access over FC, RDMA or TCP for flash arrays.
Access is restricted with zoning on FC switches and LUN masking on the array, so each server sees only its own volumes. Servers usually have two paths (multipathing) to two separate fabrics.
| DAS | NAS | SAN | |
|---|---|---|---|
| Access type | Block | File | Block |
| Protocols | SATA, SAS, NVMe | SMB, NFS | FC, iSCSI, NVMe-oF |
| Shared? | No (one server) | Yes, many clients | Yes, many servers |
| Cost and skills | Low | Low to medium | Medium to high |
| Good for | Single servers, HCI | File shares, backups | Databases, VM clusters |
Tip: none of these is a backup. RAID, snapshots and replication protect against hardware failure, not against deletion or ransomware. Keep separate, offline or immutable backup copies.
Practice
Which option lets a Windows file share be opened by 200 users at once?
What is a LUN?
Why is iSCSI traffic usually placed on a separate VLAN or network?
Key takeaways
- Block storage gives a server a raw disk; file storage shares finished files.
- DAS is fast and simple but tied to one server.
- NAS shares files over SMB or NFS on the normal network.
- SAN gives shared block storage over FC, iSCSI or NVMe-oF with zoning and masking.
- RAID, snapshots and replication are not backups.
Original content written by Mohamed Fayas for FM TecHub. © 2026 FM TecHub. You're welcome to share a link to this page; please don't copy the text elsewhere without permission.