Bài giảng Network - Chapter 14

Chapter Overview Determining Network NeedsProviding Fault ToleranceCollecting Essential Information 1Why Does the Organization Want a New Network Installed?You might be providing a network for a new installation that has no existing equipment.You might be asked to network a group of existing stand-alone computers.The organization might have an existing network that it wants to upgrade to a new or different technology. 2What Services Does the Organization Want the Network to Provide? At the most basic level, organizations usually want their users to be able to access shared drives and printers and connect to the Internet.Heads of organizations and users often know what they want in a network but do not understand the technical requirements and implementation issues.In addition to talking to the heads of organizations, it is a good idea to talk with the people who will use the network. 3Evaluating the Installation Site A proper site evaluation helps you to choose What type of network to installWhat network medium to useHow to install the network 4Evaluating Distances Between Components Know the maximum distances supported by the protocols you will use.Consider the actual route that your cables will take, not just the distance between the components.Consider the obstacles between the computers that will be connected to the network.Determine where to put the back-end components, such as hubs, servers, and routers. 5Ergonomics Planning a network includes Selecting equipment designs that are suitable for the working environment Placing equipment where it will be most useful and cause the least distraction 6Environmental Conditions Be conscious of the climate conditions at all equipment locations and at all times of day.A data center containing a large number of computers, routers, and other heat-producing devices will probably need an independent climate control system to keep the room cool enough.Make sure a source of clean, consistent electrical power is available.Some networks are exposed to extreme environments, such as outdoors or industrial areas that expose the equipment to abnormal amounts of heat or cold, humidity, dust, electromagnetic interference, or chemical vapors. Some products enable computers to operate in extreme conditions. 7Sources of Interference For internal cable installations, examine the anticipated cable locations and routes for possible obstructions and sources of interference.Keep in mind that copper-based cables are highly susceptible to electromagnetic fields caused by fluorescent light fixtures, electric motors, and other types of electrical equipment.Use cable routes that avoid sources of interference.If proper routes are not available, you might have to use cable with additional shielding, or even fiber optic cable, which is not affected by electromagnetic interference. Be aware of local fire and building codes for cabling. 8Selecting Hardware For a new network installation, you should select computers that can fully support the networking tasks expected of them.If networking existing computers, you should consider their age and whether you need to upgrade them by adding memory or disk space.Compatibility is crucial when working with existing equipment—either an existing network or a group of stand-alone computers.Many hardware purchasing decisions you make are based on the protocols you choose to run, especially at the data-link layer. 9What Is Fault Tolerance? Depending on the organization, an equipment failure or other service interruption can mean lost productivity, lost revenue, and sometimes lost lives.Fault-tolerance mechanisms enable a computer or a network to continue operating despite the failure of a major component.When network functions are absolutely critical, the fault-tolerance mechanisms can be elaborate.In most cases, however, fault-tolerance mechanisms protect only a few key components from outages due to hardware or software faults. 10Mirroring Mirroring is an arrangement in which two identical hard drives connected to a single host adapter always contain identical data.The two drives appear to users as one logical drive.Whenever users save data to the mirror set, the computer writes it to both drives simultaneously.If one hard drive unit fails, the other takes over immediately until the malfunctioning drive is replaced. Many operating systems, including Microsoft Windows 2000, Microsoft Windows NT, and Novell NetWare, support disk mirroring.Disk mirroring has two main drawbacks: The server provides only half of its available disk space to users.Although mirroring protects against a drive failure, a failure of the host adapter or the computer can still render the data unavailable. 11Duplexing Disk duplexing provides a higher degree of data availability than mirroring because it uses duplicate host adapters as well as disk drives.Identical disk drives on separate host adapters maintain exact copies of the same data, creating a single logical drive.Duplexing allows the server to survive either a disk failure or a host adapter failure and still make its data available to users. 12Volumes A volume is a fixed amount of data storage space on a hard drive or other storage device.On a network server, you can create Multiple volumes on a single drive A single volume from multiple drives (a technique called drive spanning)You can use drive spanning to make all storage space on multiple drives in a server appear as a single entity.The drawback of drive spanning is that if one of the hard drives containing part of the volume fails, the whole volume is lost. 13Disk Striping Disk striping is a method in which you create a single volume by combining the storage on two or more drives and writing data alternately to each one.The computer splits each file into multiple segments and writes alternate segments to each disk. Striping speeds up data access by enabling one drive to read a segment while the other drive’s heads are moving to the next segment.If one drive in the stripe set fails, the entire volume is lost. 14RAID Redundant array of independent disks (RAID) is a comprehensive data availability technology with various levels that provide all of the functions of mirroring, duplexing, volumes, and disk striping.Higher RAID levels store error correction information along with the data, so that even if a drive in a RAID array fails, its data still remains available from the other drives.Although RAID is available as a software product that works with standard disk drives, many high-end servers use dedicated RAID drive arrays, whichConsist of multiple hard drive units in a single housingOften have hot swap capabilityHot swapping is the ability to remove and replace a malfunctioning drive without shutting off the other drives in the array, so the data is continuously available to network users during the drive repair.15RAID Levels Level Technology Function 0 Disk striping Enhances performance by writing data to multiple disk drives, one block at a time; provides no fault tolerance. 1 Disk mirroring and duplexing Provides fault tolerance by maintaining duplicate copies of all data on two drives. Disk mirroring uses two drives connected to the same host adapter, and disk duplexing uses two drives connected to different host adapters. 2 Hamming error-correcting code (ECC) Ensures data integrity by writing error-correcting code to a separate disk drive; rarely implemented. 3 Parallel transfer with shared parity Provides fault tolerance by striping data at the byte level across a minimum of two drives and storing parity information on a third drive. If one of the data drives fails, its data can be restored by using the parity information. 16RAID Levels (Cont.) Level Technology Function 4 Independent data disks with shared parity Identical to RAID 3, except that the data is striped across the drives at the block level. 5 Independent data disks with distributed parity Provides fault tolerance by striping both data and parity across three or more drives instead of using a dedicated parity drive, as in RAID 3 and RAID 4. 6 Independent disks with two-dimensional parity Provides additional fault tolerance by striping data and two complete copies of the parity information across three or more drives. 7 Asynchronous RAID Proprietary hardware solution that consists of a striped data array and a separate parity drive, plus a dedicated operating system that coordinates the disk storage activities. 17RAID Levels (Cont.) Level Technology Function 10 Striping of mirrored disks Combines RAID 0 and RAID 1 by striping data across mirrored pairs of disks, thus providing both fault tolerance and enhanced performance. 53 Striped array of arrays Stripes data across multiple RAID 5 arrays, providing the same fault tolerance as RAID 5 with additional performance enhancement. 0+1 Mirroring of striped disks Combines RAID 0 and RAID 1 in a different manner by mirroring the data stored on identical striped disk arrays. 18NAS Network attached storage (NAS) uses a dedicated storage appliance that connects directly to the network and contains its own embedded operating system.NAS is essentially a multiplatform file server.Computers on the network can access the NAS appliance in a variety of ways. 19SANs A Storage Area Network (SAN) is a separate network installed at a local area network (LAN) site that connects servers to disk arrays and other network storage devices.SANs make it possible to use dedicated storage hardware arrays without overloading the client network with storage-related traffic.SANs typically use the Fibre Channel protocol to communicate, but they can theoretically use any network medium and protocol. 20Novell NetWare SFT III NetWare SFT III was one of the first commercially successful server duplication technologies.NetWare SFT III is a version of NetWare that consists of two copies of the network operating system, plus a proprietary hardware connection that links the two separate server computers. The servers run an application that synchronizes their activities.For example, when a user saves data to one server volume, the data is written to both servers at the same time.If one of the servers should malfunction for any reason, the other server instantly takes its place. 21Novell NetWare SFT III Connects Two Servers 22Clustering Clustering is a technique for interconnecting multiple computers to form a unified computing resource and provide fault tolerance.A cluster can also Distribute the processing load for specific tasks among the various computers Balance the processing load by allocating client requests to different computers in turn To increase the cluster’s speed and efficiency, you can connect another computer to the group to add its capabilities to those of the others. Both Microsoft and Novell support clustering.Microsoft Windows 2000 Advanced Server and Microsoft Windows NT 4.0 Enterprise Edition Novell NetWare Cluster Services for NetWare 5.1 23Servers Connected in a Cluster 24Network Redundancy 25Standardizing Workstation Configurations Creating a standard workstation configuration simplifies the troubleshooting process, because all of the computers are functionally the same.A workstation configuration can include any or all of the following elements:Which applications are installed Where the applications are installed Where the users will store data files Drive letter mappings for shared network drives Local drive sharing parameters Printer connections The ideal situation is to make new workstations completely identical, except for parameters that must be unique. If several users have different requirements, you might need to create several different workstation configurations. 26Factors in Selecting IP Addresses How many computers are there?How many network segments are there?Will you connect the network to the Internet?If you will connect the network to the Internet, how will you do it?Will your new computers interact with existing computers? 27Additional TCP/IP Configuration Issues What routers should your workstations use as their default gateways?Which Domain Name System (DNS) servers should the workstations use?Should you run Windows Internet Name Service (WINS)? 28Creating Accounts To assign computer names and account names, develop a formula and stick to it. You can create computer names that use codes to represent the subnet the computer is on or the physical location of the computer in the building. Do not assign computer names based on the names of their users because you do not want to change the name whenever someone new uses the computer. To assign user account names, you can combine the user’s initials and several letters of the first and last name.Set a policy for the administrative accounts for your network.Decide which groups or organizational units you want to create to administer the accounts most efficiently. 29Chapter Summary Determining network needs Consult with both management and staff to determine what network services are required. Evaluate the site where the network will be to determine what type of hardware to install, what network medium to use, and how to install the network. Check distances between network components, environmental conditions, local building codes, and possible sources of structural and electromagnetic interference. Select network hardware carefully to ensure that all products are compatible. 30Chapter Summary (Cont.) Providing fault toleranceNetworks use a variety of data storage techniques to increase the efficiency and fault tolerance of the network storage subsystem. Creating redundant paths through the network enables communications to continue, even if a cable breaks or a router fails. Collecting essential information Creating standard workstation configurations simplifies the process of supporting the computers later. Before installing the network, you must decide what Internet Protocol (IP) addresses you will use and how you will assign them.The best way to assign computer names and user account names is to develop a formula and use it consistently. 31