SAN architecture
Storage area networks( SAN) topologically represent a direct connection between a server and a storage subsystem. In principle, the various high-speed networks such as Gigabit Ethernet, ATM or Fibre Channel can be used for this task.
In the case of SANs, the Fibre Channel has become established as the network concept. Depending on the connection type, a distinction is made between three different architectures: the point-to-point connection, the Fibre Channel Arbitrated Loop( FC-AL) and the Fibre Channel Fabric. All three architectures offer throughput rates of 200 MByte/s in full duplex operation and work with copper and fiber optic cabling.
In the former connection type, point-to-point, each server is connected to each storage system using a direct link. This can still be implemented for a small number of servers and storage systems, but it imposes technical limits on larger installations because some servers and storage devices cannot tolerate more than four adapters. This architecture plays a minor role in practice.
In the second type of connection, FC-AL, larger networks are connected together in a Fibre Channel ring, in which a hub acts as a switching point between the various servers, disk storage devices and tape drives. The storage media are simply linked via the transmission medium. Up to 127 devices can be connected to such a configuration. The number is limited by the 8-bit addressing of the FC-AL protocol. The total transfer speed cannot exceed the 100 MByte/s of the Fibre Channel.
In the latter configuration, the Fibre Channel fabric, the hub is replaced by an FC switch (FC-S). The topology is star-shaped, although it can be a logical ring structure. This concept offers advantages in both speed and security.
A switching-based storage network requires a huge amount of management effort with clean physical allocation, with performance monitoring, fault reporting systems and predictive capacity planning.