Backup

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In computing, backup represents the process of copying data in order to have an additional copy should the original source be lost. When a backup copy is present, if the original source is damaged to a significant extent or lost completely, the backup copy can be used instead, in a process known as Data recovery or Restore

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Strategies and methods

There are several strategies and methods involved in using backups. The most common ones include:

  • Continuous, automatic and cyclical backups. Manual backups are still used, but often in conjunction with automatic backups. These should be standardized and closely followed.
  • Creating several backup copies and physically depositing them in various places, in order to avoid data loss due to incidents like fires and to improve the security of backups.
  • Storing the compressed data in an uncompressed form, since they are easier to recover if the backup media is also damaged. However, this should be considered: if the backup space is sparse, it's better to compress data than to backup less often.
  • Using incremental backup wherever possible to minimize the performance loss in work environments.
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Media

Today, the most common backup media types are high-capacity storage devices like magnetic tape and hard disks. When the data volume is not that high, ordinary optical disks like CD-R or DVD-R can be used. Remote backups can be used where network bandwidth is not a problem.

Most home users prefer using CDs for backups, as CDs have a capacity high enough to store significant amounts of data (700 or 800 MB) and are also quite cheap.

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Characteristics

A backup strategy can be described by six characteristics or metrics:

  • Backup Window, which is the amount of time needed to copy a data set to the backup media. Traditional backup systems require that the data remains unchanged during backup windows, but newer methods, like incremental backup, do not require this anymore.
  • Restore Time is the amount of time needed for the data set to be copied back to the initial source from the backup media.
  • Recovery Point Objective represents the exact moment when the backed up data will reflect, or, more simply, the amount of roll-back time experienced when the data set is restored.
  • Retention Time represents the amount of time in which a data set remain available and can be restored. Common practice require at least three backed up data sets to be present at a certain moment.
  • Backup Validation is a process through which the backed up data is compared to the original data in order to spot any possible difference. This is especially important in places where the data set is very sensible to even slight modifications.
  • Open File Backup refers to the ability of backing up a file while opened and used by another application.
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