2. Introduction to Computer Networks Introduction to Computer Networks

3. Avoiding Data Loss This lesson presents an overview of the possible causes of data loss and how to protect the network against them.

4. Data Protection The causes of a network disaster inlude:The causes of a network disaster inlude: Component failure.Component failure. Computer viruses.Computer viruses. Data deletion and corruption.Data deletion and corruption. Fire caused by arson or electrical mishaps. Fire caused by arson or electrical mishaps. Natural disasters, such as lightning, floods earthquakes. Natural disasters, such as lightning, floods earthquakes. Power-supply failure and power surges. Power-supply failure and power surges. Theft and vandalism.Theft and vandalism.

5. Data Protection & Recovery There are several ways to prevent or recover from data loss, including:There are several ways to prevent or recover from data loss, including: Tape backup systems.Tape backup systems. An uninterruptible power supply (UPS).An uninterruptible power supply (UPS). Optical drives and disks. Optical drives and disks. Fault-tolerant systems.Fault-tolerant systems.

6. Tape Backup The simplest, most inexpensive way to avoid disastrous loss of data is to implement a schedule of periodic backups with storage offsite.The simplest, most inexpensive way to avoid disastrous loss of data is to implement a schedule of periodic backups with storage offsite. Using a tape backup is still one of the few simple and economical ways to ensure that data remains safe and usable.Using a tape backup is still one of the few simple and economical ways to ensure that data remains safe and usable. A secure backup strategy minimizes the risk of losing data by maintaining a current backup— copies of existing files—so that files can be recovered if harm comes to the original data.A secure backup strategy minimizes the risk of losing data by maintaining a current backup— copies of existing files—so that files can be recovered if harm comes to the original data.

7. Implementing a Backup System Complete backups make restoring disk configurations much easier, but can require multiple tapes if there are large amounts of data.Complete backups make restoring disk configurations much easier, but can require multiple tapes if there are large amounts of data. Backing up individual files and directories might require fewer tapes, but could require the administrator to manually restore disk configurations.Backing up individual files and directories might require fewer tapes, but could require the administrator to manually restore disk configurations. Critical data should be backed up according to daily, weekly, or monthly schedules, depending on how critical the data is and how frequently it is updated.Critical data should be backed up according to daily, weekly, or monthly schedules, depending on how critical the data is and how frequently it is updated.

8. Testing and Storage Experienced administrators test the backup system before committing to it.Experienced administrators test the backup system before committing to it. They perform a backup, delete the information, restore the data, and attempt to use the data. They perform a backup, delete the information, restore the data, and attempt to use the data. The administrator should test the backup procedures regularly to verify that what is expected to be backed up is actually being backed up.The administrator should test the backup procedures regularly to verify that what is expected to be backed up is actually being backed up.

9. Maintaining a Backup Log Maintaining a log of all backups is critical for later file recovery.Maintaining a log of all backups is critical for later file recovery. A copy of the log should be kept with the backup tapes, as well as at the computer site.A copy of the log should be kept with the backup tapes, as well as at the computer site. The log should record the following information:The log should record the following information: Date of backup, Tape-set number Type of backup performed Which computer was backed up Which files were backed up Who performed the backup, etc. Date of backup, Tape-set number Type of backup performed Which computer was backed up Which files were backed up Who performed the backup, etc.

10. Installing the Backup System Backing up across the network is the most efficient way to back up multiple systems.Backing up across the network is the most efficient way to back up multiple systems. Network traffic is reduced by backing up to a separate segment.Network traffic is reduced by backing up to a separate segment.

11. Uninterruptible Power Supply (UPS) An UPS is an automated external power supply designed to keep a server or other device running in the event of a power failure.An UPS is an automated external power supply designed to keep a server or other device running in the event of a power failure. The standard UPS provides a network with two crucial components:The standard UPS provides a network with two crucial components: A power source to run the server for a short timeA power source to run the server for a short time A safe shutdown management serviceA safe shutdown management service

12. Fault-Tolerant Systems (1) Fault-tolerant systems protect data by duplicating data or placing data in different physical sources, such as different partitions or different disks.Fault-tolerant systems protect data by duplicating data or placing data in different physical sources, such as different partitions or different disks. Data redundancy allows access to data even if part of the data system fails.Data redundancy allows access to data even if part of the data system fails. Fault-tolerant systems should never be used as replacements for regular backup of servers and local hard disks.Fault-tolerant systems should never be used as replacements for regular backup of servers and local hard disks.

13. Fault-Tolerant Systems (2) Fault-tolerant systems offer these alternatives for data redundancy:Fault-tolerant systems offer these alternatives for data redundancy: Disk stripingDisk striping Disk mirroringDisk mirroring Sector sparingSector sparing Mirrored drive arraysMirrored drive arrays ClusteringClustering

14. Redundant Array of Independent Disks (RAID) (1) Fault-tolerance options are standardized and categorized into levels. These levels are known as redundant array of independent disks (RAID):Fault-tolerance options are standardized and categorized into levels. These levels are known as redundant array of independent disks (RAID): Level 0—Disk StripingLevel 0—Disk Striping

15. Redundant Array of Independent Disks (RAID) (2) Level 1—Disk MirroringLevel 1—Disk Mirroring

16. Redundant Array of Independent Disks (RAID) (3) Level 2 — Disk Striping with ECCLevel 2 — Disk Striping with ECC When a block of data is written, the block is broken up and distributed (interleaved) across all data drives.When a block of data is written, the block is broken up and distributed (interleaved) across all data drives. Error-correction code (ECC) requires a larger amount of disk space than parity-checking methods, discussed under Level 3.Error-correction code (ECC) requires a larger amount of disk space than parity-checking methods, discussed under Level 3.

17. Redundant Array of Independent Disks (RAID) (3) Level 3—ECC Stored As ParityLevel 3—ECC Stored As Parity Disk striping with ECC stored as parity is similar to level 2.Disk striping with ECC stored as parity is similar to level 2. The term parity refers to an error-checking procedure in which the number of 1s must always be the same—either odd or even—for each group of bits transmitted without error.The term parity refers to an error-checking procedure in which the number of 1s must always be the same—either odd or even—for each group of bits transmitted without error. In this strategy, the ECC method is replaced with a parity-checking scheme that requires only one disk to store parity data.In this strategy, the ECC method is replaced with a parity-checking scheme that requires only one disk to store parity data.

18. Level 3—ECC Stored As Parity

19. Redundant Array of Independent Disks (RAID) (4) Level 4—Disk Striping with Large BlocksLevel 4—Disk Striping with Large Blocks This strategy moves away from data interleaving by writing complete blocks of data to each disk in the array.This strategy moves away from data interleaving by writing complete blocks of data to each disk in the array. The process is still known as disk striping, but is done with large blocks. A separate check disk is used to store parity information. The process is still known as disk striping, but is done with large blocks. A separate check disk is used to store parity information. Each time a write operation occurs, the associated parity information must be read from the check disk and modified.Each time a write operation occurs, the associated parity information must be read from the check disk and modified.

20. Level 4—Disk Striping with Large Blocks

21. Redundant Array of Independent Disks (RAID) (5) Level 5—Striping with ParityLevel 5—Striping with Parity The data and parity information are arranged so that the two are always on different disks.The data and parity information are arranged so that the two are always on different disks. A parity stripe block exists for each stripe (row) across the disk. A parity stripe block exists for each stripe (row) across the disk. The parity stripe block is used to reconstruct data for a failed physical disk.The parity stripe block is used to reconstruct data for a failed physical disk. Striping with parity is currently the most popular approach to fault-tolerant design.Striping with parity is currently the most popular approach to fault-tolerant design.

22. Redundant Array of Independent Disks (RAID) (6) Level 10—Mirrored Drive ArraysLevel 10—Mirrored Drive Arrays RAID level 10 mirrors data across two identical RAID 0 drive arrays.RAID level 10 mirrors data across two identical RAID 0 drive arrays.

23. Redundant Array of Independent Disks (RAID) (7) Sector SparingSector Sparing This feature automatically adds sector-recovery capabilities to the file system while the computer is running.This feature automatically adds sector-recovery capabilities to the file system while the computer is running.

24. Microsoft Clustering Microsoft Clustering is Microsoft's implementation of server clustering.Microsoft Clustering is Microsoft's implementation of server clustering. The term "clustering" refers to a group of independent systems that work together as a single system.The term "clustering" refers to a group of independent systems that work together as a single system. Should a system within the cluster fail, the cluster software will disperse the work from the failed system to the remaining systems in the cluster.Should a system within the cluster fail, the cluster software will disperse the work from the failed system to the remaining systems in the cluster.

25. Optical Drives and Disks In optical technology, data is stored on a rigid disk by altering the disk's surface with a laser beam.In optical technology, data is stored on a rigid disk by altering the disk's surface with a laser beam. As the technology evolves from the original read- only and read-write CD-ROMs to the new DVD technologies, these devices are being used more and more to store large amounts of retrievable data.As the technology evolves from the original read- only and read-write CD-ROMs to the new DVD technologies, these devices are being used more and more to store large amounts of retrievable data. Optical-drive manufacturers provide a large array of storage configurations that are either network- ready or can be used with a network server.Optical-drive manufacturers provide a large array of storage configurations that are either network- ready or can be used with a network server.

26. Disaster Recovery The best way to recover from a disaster is to prevent it from happening in the first place.The best way to recover from a disaster is to prevent it from happening in the first place. Not all disasters can be prevented.Not all disasters can be prevented. When considering disaster protection, you will need a plan for hardware, software, and data.When considering disaster protection, you will need a plan for hardware, software, and data. Physical components of a network can be easily replaced and are usually covered by some form of insurance, but data is highly vulnerable to disaster.Physical components of a network can be easily replaced and are usually covered by some form of insurance, but data is highly vulnerable to disaster.