A Storage Area Network (SAN) is a way of connecting computers and storage devices so computers have fast, shared access to files while making it easy for administrators to expand storage capacity.
An Xsan SAN consists of:
Shared data volumes
RAID systems that provide storage space that’s protected from disk failure
At least one computer acting as a metadata controller that combines RAID arrays and presents their storage to clients as volumes that behave like local disks
Client computers that access storage in accordance with established permissions and quotas
Underlying Fibre Channel and Ethernet networks
Shared SAN volumes
A user or application on a client computer accesses shared SAN storage the way they would access a local volume. Xsan volumes are logical disks made up of pools of RAID arrays.
Metadata controllers
When you set up an Xsan SAN, you assign at least one computer to act as the metadata controller. The controller manages volume metadata, maintains a file system journal, and controls concurrent access to files. Metadata includes such information as where files are stored and what portions of available storage are allocated to new files.
To guarantee volume availability, a SAN should include more than one metadata controller. If the active controller fails, a standby controller takes over.
Clients
The computers that users or apps use to access SAN volumes are called clients. Clients exchange metadata with controllers over an Ethernet network but use Fibre Channel to send and retrieve file data to and from the RAID systems that provide storage for the volumes.
Fibre Channel network connection
Xsan moves data between clients and SAN volumes over high-speed Fibre Channel connections. Controllers also use a Fibre Channel connection to move metadata to and from the volume.
Xsan can take advantage of multiple Fibre Channel connections between clients and storage. Xsan can alternate between connections for each read and write, or it can assign each RAID array in a volume to a connection when the volume is mounted.
Ethernet network connection
Xsan controllers and clients exchange file system metadata over an Ethernet network. (Controllers use Fibre Channel to read and write metadata on a volume.)
To prevent Internet or intranet traffic from interfering with metadata communications, you can optionally set up separate public (Internet) and private (metadata) Ethernet networks.