SAN and FCP

Storage area networks (SANs) are specialized networks dedicated to the transport of mass storage data.

SANs are typically used to connect large servers in enterprise environments with storage systems and tape libraries. These specialized networks provide reliable and fast data paths between the servers and their storage devices. Major advantages of a SAN include:

Consolidating storage devices
Physically separating storage devices from the servers
Sharing storage devices among different servers

A typical SAN consists of the following components:

Servers
Storage devices
Switches

Today the most common SAN technology used is the Fibre Channel Protocol (FCP). Within this technology the traditional SCSI protocol is used to address and transfer raw data blocks between the servers and the storage devices. This is in contrast to other storage communication protocols like the Common Internet File System (CIFS) or the Network File System (NFS) which operate on file level.

Figure 1 shows how the zfcp device driver allows you to connect Linux on z Systems™ to a SAN using FCP.

Figure 1. SAN connected to mainframe through FCP

This graphic is described in the text surrounding it

The mainframe in Figure 1 is equipped with a hardware feature that has at least one channel configured as an FCP channel. This FCP channel provides the physical connection to the SAN. In a typical mainframe environment, multiple FCP channels are configured to increase the I/O bandwidth and improve data availability. Multiple operating system instances can share one FCP channel.

Storage devices used in SANs are disk storage systems and tape libraries. A disk storage system comprises multiple hard drives combined into one or more RAID arrays and a storage controller communicating through one or more HBAs with the SAN. The usage of RAID arrays and multiple HBAs increases the I/O bandwidth and improves data availability. The RAID arrays are used to store the user data and the controller is responsible for providing functions such as I/O processing, data caching, and system management. The storage available on the RAID arrays is usually divided into smaller units that are then accessible as a single, logical storage device, called a logical unit number (LUN), from the SAN.

Fibre Channel switches connect multiple servers with their storage devices to form a fiber channel fabric. A fiber channel fabric is a network of Fibre Channel devices that allows communication and provides functions such a device lookup or access control. To address a physical Fibre Channel port within a Fibre Channel fabric each port is assigned a unique identifier called worldwide port name (WWPN).