Comparing SAN and NAS storage

NAS: file level

Network Attached Storage serves files. The file system lives on, and is managed by, the storage system.

It typically rides the existing Ethernet data network, plain NICs everywhere.

SAN: block level

A Storage Area Network serves raw blocks. The client sees its allocation as if it were a local disk and manages the file system itself.

Traditionally it’s a separate dedicated storage network (its own switches, sometimes its own cabling and adapters), alongside the client-facing Ethernet.

Because a SAN LUN looks exactly like a local drive, boot from SAN works, enabling diskless servers. Not possible with NAS.

The split in one line

NAS: “here’s a file share, I’ll handle the file system.” SAN: “here’s a disk, you handle the file system.”

Protocols

• NAS: SMB/CIFS and NFS.
• SAN: Fibre Channel, iSCSI, FCoE, and NVMe over Fabrics.

Early arrays did one or the other. Modern “unified” storage systems speak both.