The exchange of data between servers and storage devices in a SAN takes place by using the fibre channel technology. The fiber channel technology is an American National Standard Institute (ANSI)-standard technology that is used for data transmission between servers and storage devices in a SAN. This technology enables the servers and storage devices in a SAN to communicate at a speed of up to 1 Gbps (100 MBps or 200 MBps) by using dedicated channels called data paths. This technology uses various protocols, such as Small Computer System Interface (SCSI) and Internet Protocol (IP), to enable the servers and storage devices to communicate with each other. The fibre channel technology is implemented in a SAN by using various hardware components, which are as follows:

I Host Base Adapter (HBA): Refers to the interface card that provides I/O processing and connectivity between the servers and storage devices connected through a SAN in an enterprise.
 SAN components: Refers to the connectivity devices, such as hubs, switches, and routers, which enable data transfer between the servers and storage devices in an enterprise.

Storage fabric: Refers to the cables used for connecting servers, storage devices, and SAN components to form the SAN environment. These cables can be optical fibers or copper wires.

Implementing a SAN in an enterprise by using fiber channel technology provides various benefits,

which are as follows:

1. Improves data availability and speed of data access by providing multiple data paths between the servers and storage devices in an enterprise.
2. Enables network administrators to perform fast backup and recovery operations. Fast data backup and recovery is possible because the data is transferred across a SAN at the speed of 100 MBps. In addition, SANS also enable network administrators to take back up directly from the storage disks of servers to the tape libraries.
3. Enables multiple servers to share a common set of storage devices, such as disk arrays and tapes, to improve the resource utilization of the storage devices.
4. Enables multiple servers to concurrently access the same tile from a storage device. This improves the speed at which the servers can access data hem the storage devices. 
5. Enables network administrators to add storage resources and servers to an enterprise when the storage requirement of the enterprise increases.

SANS provide the following features that enable the servers and storage devices in an enterprise to exchange data efficiently:

High bandwidth:
Enables servers and storage devices to exchange data at the speed of 100 MBps. This ensures that backup of data stored on servers can be taken at a high speed.

Scalability:
 Enables network administrators of an enterprise to increase the number
of storage devices connected to a SAN, when the storage requirement of the
enterprise increases.

Flexibility:
Enables network administrators of an enterprise to logically partition the storage space on a device into various parts,
called logical units and assign these logical units to different servers.
For example, network administrators can create multiple logical units on disk drives so that multiple database servers can share the same disk drive.
Using logical units to provide storage space to users ensures that the storage devices can be used according to requirement.

Globally available storage:
Enables users in an enterprise to access the storage devices from any location. This ensures that the
employees of an enterprise can access data stored in the enterprise while working at client sites.
Data sharing: Enables multiple servers to concurrently access a single file stored on a storage device. This improves the speed of data access from the storage devices.

System Administrator

The System Administrator (SA) is primarily responsible for the smooth operation of the System.It is a SA s job to switch on the system console.(The machine on which the Operating System resides , also known as the server machine.) The SA also creates users and groups of users for the system and tasks backup to prevent loss of data due to system break down.In Linux the SA is also known as the root user. The SA has all the right for the Linux System.

File Owner

The User who creates a file is said to be the owner of that file.The owner of a file can perform any operation on that file coping , deleting ,editing.

Group Owner

Consider the following Situation.
a project team of 5 people from the Esoft Metro Campus is working on a software development project for a private detective agency. An analyst heads the team. The other four members are programmers.The team is working on a Linux System.Each programmers has been given a few programs to develop.the data provided by the detective agency is of a highly confidential nature.and so the data file has been created in the analyst's HOME directory. one programmer may have to link(join) a program to another programmers programming in order to test the program.
In this situation each programmer is the file owner of his or her own program files.Each program,how ever also belongs to  the other programmers.so that they can use it for linking to the file or directly access the file. The Project team of five users is said to be the Group owner for the file . In Linux It is possible to define the users who will belongs to a group. a group of users are also given a name ,  just as a user is given a name.

Other Users

 In the example of the Esoft Metro Campus , all the users of the System who are not members of the project groups are referral to as other users for the  files of that group.Their Users are users who do not belongs to the particular group. For Example, the Users belongs to the finance department could be treated as other users for the payroll department.

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The ring topology connects the nodes on a network through a point to poinr connection. Consequently, no end points exist in this type of setup.
The following figure shows a typical ring-based setup.

In the preceding figure all computers are connected in  a ring-like layout.As a result,similar to the bus topology, the main cable is the only transmission path.How ever, unlike the bus topology, data packet can ravers only in a unidirectional format.
When a node receives a data packet ,it reads the data packet and regenerates it to restore its original strength. The packet is then passed to the neighboring node. The data packet navigates the network in this format until the destination nodes receives the packet.

Advantages

Prevention of Collisions

The ring topology prevents network collisions by using the token ring access method. According to this method, if a node needs to transmit data, it must acquire a token that circulate through the ring. when the node acquire the token ,the node uses the token to transfer its data to the destination node. Until the current node releases the token other node cannot transmit data and must wait for their turn to acquire the token. As a result, the possibility of any collision in this step is 0.

Ease in troubleshooting and maintenance

Its easy to locate cable faults in ring setup.In cable related fault, the nodes that is next to failed cable segment can indicate the fault when it fails to receive a signal within the specified time limit.

Limitations

High Risk of network Failure

On a ring network, the nodes are connected through a point to point connection. If one of node on the network malfunctions , the entire network stops functioning.

Expensive Setup and Installation

The Device and Cabling  required to setup a ring network are more expensive than any other topology.

The star topology connects nodes over a network using a central control unit called the Concentrater(Hub), Concentrater can be a Hub, a switch or a router. The hub is a device that transmits information from one node to another.
The following figure shows a typical star topology setup

In preceding figure , All computers are connected through a hub. If a computer transmit data to an another computer , Each data packet from source computer is firstly sent to the hub.The hub ,in turn, sends data packets to destination computer.

Advantages

Higher Scalability
 Can easily add nodes to a star based network by attaching the required node to the hub. How ever the number of nodes that you can connect to the hub depends on the capacity of the hub.

Ease in troubleshooting and maintenance.
It is easy to locate fault in a star setup.If a node becomes faulty, It does not affect the working of the hub, which,in turn,does no affect the other nodes of the network

Limitations

High Cost of Installation

Setting up a star topology requires a lot of cabling because all the nodes have to connect to the hub. in addition the hubs are very expensive.

Single Point of Failure

The hub is a single point for handling network communication. As a result , a failure in the hub can disrupt the entire network communication.

The bus topology connects all the nodes on a network to a main cable called bus, as shown in the following figure

In the preceding figure Computers are connected through the bus, When a Computer needs to transmit data to an another computer , Is sends the data over the bus in the form of data packets. In the bus topology each packet placed on the bus contains the address of the destination node. The packet is transmitted in both directions along the bus. In other words,The data packet is sent to all the nodes in the network.Each node on the network, which receive a data packet compares the destination address of the packet with its own address. If the two address match the nodes, reads the data packet else it ignore the packet.

A device call Terminator is attached to each end of the bus As the name suggest , the terminator receives signal that have traversed through the bus and  terminates them.The termination of signals ensures that signals that have already traversed through the bus do not collide with new signals.

In the Bus topology data packets may collide if multiple nodes transmit signal at the same time. to prevent this situation, the bus topology provides a collision detection mechanism called Carrier Sense Multiple Access with Collition Ditection (CSMA/CD) . This Mechanism resolves the collisions that may occur if multiple nodes transmit data packet simultaneously.

Advantages

• Easy Installation
• Require Minimum cabling
• Relatively inexpensive
• Cost of cabling is less

Limitations

Low fault tolerance

• The Bus topology is highly prone to faults. If the bus connecting the computers malfunctions, the entire network communication is disrupted. As a result, the bus is single point of failure (SPOF) on the network

Inability to handle high network traffic

• In the bus topology, only one nod can transmit packets at any instance. If multiple nodes transmit data packets simultaneously, it leads to network collisions. As a result the higher the number of nodes on the bus, the lower is its performance. According to specifications,only 15 nodes can be connected to a bus of 30 meters.
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Lower Scalability

• Adding nodes to an existing bus topology network is difficult.To add a node to the net work, the entire network cable setup needs to be reconfigured.I addition , the length of the cable used for the topology has a physical limitation of 30 meters.It cannot expanded beyond this limit. As as a result ,the number of nodes that can be attached to the network is limited.
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Difficulty in Troubleshooting and maintenance

• If a problem occurs on a node in the bus topology , troubleshooting become time-consuming. This is because the administrator needs to check every point on the step to locate the fault.