Backup


Definition of Backup in the Network Encyclopedia.

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Backup
Backup




What is BACKUP?

Backup is simply a copy of important data. Performing regular backups is one of the main components of a company’s disaster recovery policy, and the importance of doing so cannot be stressed enough. Various occurrences can lead to data loss on a corporate network:

  • Disk failures caused by hardware failure, power outages, or improper use
  • Network problems leading to lost packets that are not acknowledged because of router congestion or other situations
  • Virus infection, resulting in corrupted files
  • Sabotage by hackers or disgruntled employees, resulting in erased data
  • Theft of hardware from the premises

Backup Strategy

To guard against these occurrences – or rather, to prepare for them, since they are, to a certain extent, inevitable – establish a disaster recovery policy that includes a reliable backup plan. In today’s business world, where data is the lifeblood of the enterprise, a comprehensive plan is essential.



A Backup Strategy is a plan for performing backups to ensure against data loss. Backup strategies should take the following into account:

  • The various backup types that can be performed
  • The need to archive tapes for long-term data security
  • The time needed to perform backups and restores
  • The cost of tapes
  • The cost of losing data

There is no one right way to implement a backup strategy for resources on a network of computers. To select the best backup strategy for your network, you must consider each of the items in the preceding list and balance them against each other. Your strategy should be simple, efficient, and reliable. The following table shows some examples of backup strategies.

Possible Backup Strategies

Backup StrategyAdvantagesDisadvantages
Normal backups Monday through Friday.Most secure – every tape contains all backed up filesLongest time to back up
Normal backup Monday; differential backups Tuesday through Friday.Less time to restoreMore time to back up
Normal backup Monday; incremental backups Tuesday through Friday.Less time to back upMore time to restore
Use a separate tape for each weekday, and archive Monday’s full backup tape weekly or monthly.Less chance of data lossHigher cost, since more tapes are needed
Use the same tape for each weekday, and archive the tape each week or month.Cheaper-only one tape required per week or monthGreater chance of data loss, since using only one tape

The following steps are recommended when creating such a plan:

  • Decide what kind of backup storage devices to use. Options range from small digital audio tape (DAT) drive units capable of backing up several gigabytes of data, to large automated tape libraries capable of handling terabytes of centralized data storage. Other backup options include optical storage libraries and removable disks such as Iomega’s Zip drive disks or Imation SuperDisk disks.
  • Decide whether to back up servers with dedicated, locally connected storage devices or over the network to centralized backup libraries. Network backup systems suffer from a single point of failure (the network itself) but are simpler to administer than a multitude of individual backup units.
  • Decide whether individual users’ workstations should also be backed up. A more cost-effective option is to educate users to always save their work on a network share located on a server that is regularly backed up.
  • Decide how to secure the storage of backup tapes and other media. Will duplicate copies be stored both on site (for easy access if a restore is needed) and off site (in case the company’s building burns down)? Make sure the storage facilities are climate controlled and secure.
  • Decide what kind of backup strategy to employ. A backup strategy is a combination of a backup schedule and various backup types, including normal, copy, incremental, differential, and daily copy backup types. Also consider whether you will verify all tapes immediately after each backup is performed.
  • Assign various aspects of the backup procedure to the responsible party. One option some companies now use is to back up data over the Internet to a third-party backup service provider that stores and maintains the backed-up data. This method involves issues of trust and of the Internet connection as a point of failure.
  • Test backups periodically to ensure that they are actually readable. Nothing is worse than thinking you have a backup when in fact it is unreadable.



To enable administrators to perform regular backups, Microsoft includes backup utilities with all versions of Microsoft Windows, such as the Backup tool in Windows 2000.

Backup Type

Backup Type is a particular method for performing a backup of files and directories. Each type of backup has a different function in an overall backup plan. Most network backup software (such as Microsoft Windows NT Backup and Windows 2000 Backup) supports five backup methods:

  • Normal backup: Backs up everything that is selected to be backed up. Normal backups are the fastest and easiest to restore. Normal backups are sometimes referred to as “full backups.” Use a normal backup when you want to ensure that all your critical system and data files are backed up in a single operation. If your backup cycle consists only of normal backups and you need to perform a restore, you need to use only the most recent normal backup to do so. (Learn more)
  • Copy backup: Primarily used to produce an additional copy of a backup—for example, a copy to send to the accounting department for monthly archiving and reporting. While a copy backup backs up the same files as a normal backup, there is a difference between the two operations. Performing a normal backup clears the archive bit on each backed up file and marks them as having been backed up. A copy backup, however, does not modify the archive bit on the files backed up. In other words, you can perform a copy backup at any time in a backup cycle without interrupting the cycle in any way—the copy backup is distinct from the backup cycle and is not required when a restore is performed from the cycle’s set of tapes. (Learn more)
  • Incremental backup: Backs up only files that have been created or modified since the last normal or incremental backup. Files that are backed up in an incremental backup have their archive attributes cleared to indicate that they have been backed up. Using a combination of normal and incremental backups takes less time and uses less storage space than performing only normal backups. However, if you need to perform a restore, you typically need to use the normal backup plus every incremental backup from the current backup cycle to do so. (Learn More)
  • Differential backup: Copies those files that have been created or changed since the last normal or incremental backup. Files that are backed up by a differential backup do not have their archive attributes cleared, which means that these files will be backed up again in any succeeding differential backups. Differential backups are cumulative with regard to changes—that is, each differential backup in a given backup cycle contains all the files from the last differential backup, plus any files that have been modified since the last differential backup. Thus, if you need to perform a restore, you will typically need to use only the normal backup and the most recent differential backup from the current backup cycle to do so. (Learn more)
  • Daily copy backup: Copies all files that have been modified on the day the daily copy backup is performed. This method is sometimes used to make a copy of all files a user worked on in a day so that he or she can take them home to work on. Like a copy backup, the daily copy backup does not modify the archive bit of the files backed up; therefore, the daily copy backup does not interrupt the backup cycle in any way. 




Backup Operations effects

Different types of backup operations have different effects on the archive attributes of the files and directories they back up. A backup operation marks the archive attribute by clearing it to indicate that the file has been backed up. If the file is later modified in some way, its archive attribute is set (unmarked). This next table shows what each type of backup operation does to the archive attribute:

Effects of Backup Operations on the Archive Attribute

Backup TypeArchive Attribute
NormalCleared
CopyNo effect
IncrementalCleared
DifferentialNo effect
Daily copyNo effect

Equipment you can buy for backing up your hard drive:

See also:




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