What is 'Networked Storage'?

Networked storage falls into general classes: storage area networks (SANs) and network-attached storage (NAS), which have many similarities.

SANs (top) enable servers to share logical disk volumes over a network specially designed for transferring disk “blocks.” In this scenario, two servers (A and B) and a backup server are connected to two different storage controller/disk array devices via a dedicated storage network, which today is most likely to be Fibre Channel. Each server has one or more Fibre-Channel host bus adapters (HBAs) connecting it to the SAN. Each application server stores its data on one or more storage volumes that are addressed using Logical Unit Numbers (LUNs), and that live within Storage Controller/Disk Arrays. Each server reads and writes “block level” disc requests only to its own LUNs and manages the file system on each. In this example, Server A “owns” LUN 1, while Server B owns LUNs 2 and 3. The Backup Server can copy data directly from the application servers’ LUNs to a tape storage system also connected to the SAN (LUN 4). If the storage controllers support “snapshots,” the applications need not be stopped during backup; all data can be backed up in a consistent state directly from storage without affecting the application servers. Servers that are running Windows .NET Server can even boot from a SAN volume and store all system information (such as the Registry) there.