7.6. Storage Area Networks and Network-Attached Storage

Storage area networks (SANs) and network-attached storage (NAS) are two related, but very different, ways to attach external file storage devices to a server. A SAN exposes a block-level interface that a server sees as being directly attached, while a NAS device exposes a file-based protocol such as NFS or SMB. A SAN is usually connected to the server via the Fibre Channel Protocol (FCP) or iSCSI, while a NAS device is connected via a standard network connection.

7.6.1. Storage Area Networks

The benefits of using a SAN include more flexible storage management and the ability to scale storage. Many SAN solutions also have special features such as a snapshot capability and support for integrated continuous backups. They permit a server to access a very large number of hard drives—often 50 or more—and typically have very large, intelligent caches to buffer writes. The block-level interface they export appears to the server as logical unit numbers (LUNs), or virtual volumes. Many SANs also allow multiple nodes to be "clustered" to get better performance.