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Note for Computer Network - CN By New Swaroop

  • Computer Network - CN
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  • University of mysore - Gangotri
  • Computer Science Engineering
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MODULE – 2 Storage Networking Technologies Chapter 5 Fibre Channel Storage Area Networks Direct-attached storage (DAS) is often referred to as a stove piped storage environment. Hosts “own” the storage, and it is difficult to manage and share resources on these isolated storage devices. Efforts to organize this dispersed data led to the emergence of the storage area network (SAN). SAN is a high-speed, dedicated network of servers and shared storage devices. 5.1 Fibre Channel: Overview The FC architecture forms the fundamental construct of the FC SAN infrastructure. Fibre Channel is a high-speed network technology that runs on high-speed optical fibre cables and serial copper cables. 5.3 Components of FC SAN 5.3.1 Node Ports In a Fibre Channel network, the end devices, such as hosts, storage arrays, and tape libraries, are all referred to as nodes. Each node is a source or destination of information. Each node requires one or more ports to provide a physical interface for communicating with other nodes. These ports are integral components of host adapters, such as HBA, and storage front-end controllers or adapters. In an FC environment a port operates in full-duplex data transmission mode with a transmit (Tx) link and a receive (Rx) link (see Figure 5-3). Source diginotes.in Save the Earth. Go paperless

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5.3.2 Cables and Connectors SAN implementations use optical fiber cabling. Copper can be used for shorter distances for back-end connectivity because it provides an acceptable signal-tonoise ratio for distances up to 30 meters. Optical fiber cables carry data in the form of light. There are two types of optical cables: multimode and single-mode. Multimode fiber (MMF) cable carries multiple beams of light projected at different angles simultaneously onto the core of the cable (see Figure 5-4 [a]). Based on the bandwidth, multimode fibers are classify ed as OM1 (62.5μm core), OM2 (50μm core), and laser-optimized OM3 (50μm core). In an MMF transmission, multiple light beams traveling inside the cable tend to disperse and collide. This collision weakens the signal strength after it travels a certain distance — a process known as modal dispersion. An MMF cable is typically used for short distances because of signal degradation (attenuation) due to modal dispersion. Single-mode fiber (SMF) carries a single ray of light projected at the center of the core (see Figure 5-4 [b]). These cables are available in core diameters of 7 to 11 microns; the most common size is 9 microns. In an SMF transmission, a single light beam travels in a straight line through the core of the fiber. The small core and the single light wave help to limit modal dispersion. Among all types of fiber cables, single mode provides minimum signal attenuation over maximum distance (up to 10 km). A single-mode cable is used for long distance cable runs, and distance usually depends on the power of the laser at the transmitter and sensitivity of the receiver. MMFs are generally used within data centers for shorter distance runs, whereas SMFs are used for longer distances. A connector is attached at the end of a cable to enable swift connection and disconnection of the cable to and from a port. A Standard connector (SC) (see Figure 5-5 [a]) and a Lucent connector (LC) (see Figure 5-5 [b]) are two commonly used connectors for fiber optic cables. Straight Tip (ST) is another fiber-optic connector, which is often used with fiber patch panels (see Figure 5.5 [c]). Source diginotes.in Save the Earth. Go paperless

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5.3.3 Interconnect Devices FC hubs, switches, and directors are the interconnect devices commonly used in FC SAN. Hubs are used as communication devices in FC-AL implementations. Hubs physically connect nodes in a logical loop or a physical star topology. All the nodes must share the loop because data travels through all the connection points. Because of the availability of low-cost and high-performance switches, hubs are no longer used in FC SANs. Switches are more intelligent than hubs and directly route data from one physical port to another. Therefore, nodes do not share the bandwidth. Instead, each node has a dedicated communication path. Directors are high-end switches with a higher port count and better fault tolerance capabilities. A port card or blade has multiple ports for connecting nodes and other FC switches. 5.3.4 SAN Management Software SAN management software manages the interfaces between hosts, interconnect devices, and storage arrays. The software provides a view of the SAN environment and enables management of various resources from one central console. It provides key management functions, including mapping of storage devices, switches, and servers, monitoring and generating alerts for discovered devices, and zoning 5.4 FC Connectivity 5.4.1 Point-to-Point Point-to-point is the simplest FC configuration — two devices are connected directly to each other, as shown in Figure 5-6. This configuration provides a dedicated connection for data transmission between nodes. However, the point-to-point configuration offers limited connectivity, because only two devices can communicate with each other at a given time. Moreover, it cannot be scaled to accommodate a large number of nodes. Standard DAS uses point-to-point connectivity. 5.4.2 Fibre Channel Arbitrated Loop In the FC-AL configuration, devices are attached to a shared loop. FC-AL has the characteristics of a token ring topology and a physical star topology. In FC-AL, each device contends with other devices to perform I/O operations. Devices on the loop must “arbitrate” to gain control of the loop. At any given time, only one device can perform I/O operations on the loop (see Figure 5-7). Source diginotes.in Save the Earth. Go paperless

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5.4.3 Fibre Channel Switched Fabric FC-SW is also referred to as fabric connect. A fabric is a logical space in which all nodes communicate with one another in a network. This virtual space can be created with a switch or a network of switches. Each switch in a fabric contains a unique domain identifier, which is part of the fabric’s addressing scheme. In FC-SW, nodes do not share a loop; instead, data is transferred through a dedicated path between the nodes. Each port in a fabric has a unique 24-bit Fibre Channel address for communication. Figure 5-8 shows an example of the FC-SW fabric. In a switched fabric, the link between any two switches is called an Interswitch link (ISL). ISLs enable switches to be connected together to form a single, larger fabric. ISLs are used to transfer host-to-storage data and Source diginotes.in Save the Earth. Go paperless

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