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SAN Storage

A storage area network (SAN) is a dedicated network that provides access to consolidated, block level data storage. SANs are primarily used to make storage devices, such as disk arrays, tape libraries, and optical jukeboxes, accessible to servers so that the devices appear like locally attached devices to the operating system. A SAN typically has its own network of storage devices that are generally not accessible through the local area network by other devices. The cost and complexity of SANs dropped in the early 2000s to levels allowing wider adoption across both enterprise and small to medium sized business environments.
A SAN does not provide file abstraction, only block-level operations. However, file systems built on top of SANs do provide file-level access, and are known as SAN filesystems or shared disk file systems.


The SAN fabric is built from interconnecting elements, such as FC hubs, Fc switches, routers, bridges. A SAN fabric connects workstations and computers to storage devices in a storage area network (SAN). SAN fabrics are a set of interconnected fibre channel switches, amongst which data can be physically transmitted. It is similar in concept to a network segment in a local area network. A typical Fibre Channel SAN fabric is made up of a number of Fibre Channel switches.

Storage routers differ from network routers in that the data being used uses storage protocols like FCP instead of TCP/IP.

Fibre Channel hubs are used to connect up to 126 nodes into a logical loop. All connected nodes share the bandwith of this one logical loop. Fibre Channel Arbitrated Loop (FC-AL)protocol is the most widely accepted, cost effective alternative.


Switches used for any-to-any connections: servers, storage systems, other switches, FC-ALs. Zoning for this can be:
-hardware: port based
-software: WWN based

Grouping together of multiple ports to form a virtual private storage network. Ports that are memebers of a group or zone can communicate with each other but are isolated from ports in other zones.

lsattr -El fscsi0
scsi_id      0×212500

21: Domain ID (switch id)
25: port id
00: lpar id of vio client (if we have vio environment)

(Fabric refers to a switched network (similar to ethernet) comparison to pt2pt (point to point) and al (arbitrared loop))

In the Fibre Channel switched fabric topology (called FC-SW), devices are connected to each other through one or more Fibre Channel switches. This topology allows the connection of up to the theoretical maximum of 16 million devices


There are three major Fibre Channel topologies, describing how a number of ports are connected together. A port in Fibre Channel terminology is any entity that actively communicates over the network. This port is usually implemented in a device such as disk storage, an HBA on a server or a Fibre Channel switch.

- Point-to-Point (FC-P2P): Two devices are connected directly to each other. This is the simplest topology, with limited connectivity.

- Arbitrated loop (FC-AL): In this design, all devices are in a loop or ring, similar to token ring networking.
The failure of one device causes a break in the ring. FC hubs exist to connect devices together and may bypass failed ports.

- Switched fabric (FC-SW): All devices or loops of devices are connected to Fibre Channel switches.
Similar conceptually to modern Ethernet implementations.

 Advantages of this topology over FC-P2P or FC-AL include:
- The traffic between two ports flows through the switches only, it is not transmitted to any other port.
- Failure of a port is isolated and should not affect operation of other ports.
- Multiple pairs of ports may communicate simultaneously in a fabric.



Fibre Channel does not follow the OSI model layering, but is split similarly into 5 layers, namely:

FC4 - Protocol Mapping layer, in which application protocols, such as SCSI or IP, are encapsulated into a PDU for delivery to FC2.
FC3 - Common Services layer, a thin layer that could eventually implement functions like encryption or RAID redundancy algorithms;
FC2 - Network layer, defined by the FC-PI-2 standard, consists of the core of Fibre Channel, and defines the main protocols;
FC1 - Data Link layer, which implements line coding of signals;
FC0 - PHY, includes cabling, connectors etc.;


N_port is a port on the node (e.g. host or storage device) used with both FC-P2P or FC-SW topologies. Also known as Node port.
F_port is a port on the switch that connects to a node point-to-point (i.e. connects to an N_port). Also known as Fabric port.
E_port is the connection between two fibre channel switches. Also known as an Expansion port.
EX_port is the connection between a fibre channel router and a fibre channel switch.
(On the side of the switch it looks like a normal E_port, but on the side of the router it is a EX_port.)

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