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Data Backup

In information technology, a backup or the process of backing up refers to making copies of data so that these additional copies may be used to restore the original after a data loss event. These additional copies are typically called "backups." The verb is back up in two words, whereas the noun is backup (often used like an adjective in compound nouns).

Backups are useful primarily for two purposes. The first is to restore a state following a disaster (called disaster recovery). The second is to restore small numbers of files after they have been accidentally deleted or corrupted. Data loss is also very common. 66% of internet users have suffered from serious data loss.

Since a backup system contains at least one copy of all data worth saving, the data storage requirements are considerable. Organizing this storage space and managing the backup process is a complicated undertaking. A data repository model can be used to provide structure to the storage. In the modern era of computing there are many different types of data storage devices that are useful for making backups. There are also many different ways in which these devices can be arranged to provide geographic redundancy, data security, and portability.

Before data is sent to its storage location, it is selected, extracted, and manipulated. Many different techniques have been developed to optimize the backup procedure. These include optimizations for dealing with open files and live data sources as well as compression, encryption, and de-duplication, among others. Many organizations and individuals try to have confidence that the process is working as expected and work to define measurements and validation techniques. It is also important to recognize the limitations and human factors involved in any backup scheme.

Storage, the base of a backup system

Data repository models

Any backup strategy starts with a concept of a data repository. The backup data needs to be stored somehow and probably should be organized to a degree. It can be as simple as a sheet of paper with a list of all backup tapes and the dates they were written or a more sophisticated setup with a computerized index, catalog, or relational database. Different repository models have different advantages. This is closely related to choosing a backup rotation scheme.

Storage media

Regardless of the repository model that is used, the data has to be stored on some data storage medium somewhere.

Managing the data repository

Regardless of the data repository model or data storage media used for backups, a balance needs to be struck between accessibility, security and cost. These media management methods are not mutually exclusive and are frequently combined to meet the needs of the situation. Using on-line disks for staging data before it is sent to a near-line tape library is a common example.

Selection and extraction of data

A successful back up job starts with selecting and extracting coherent units of data. Most data on modern computer systems is stored in discrete units known as files. These files are organized into filesystems. Files that are actively being updated can be thought of as "live" and present a challenge to back up. It is also useful to save metadata that describes the computer or the filesystem being backed up.

Deciding what to back up at any given time is a harder process than it seems. By backing up too much redundant data, the data repository will fill up too quickly. Backing up an insufficient amount of data can eventually lead to the loss of critical information.

Files

Filesystems

Live data

If a computer system is in use while it is being backed up, the possibility of files being open for reading or writing is real. If a file is open, the contents on disk may not correctly represent what the owner of the file intends. This is especially true for database files of all kinds. The term fuzzy backup can be used to describe a backup of live data that looks like it ran correctly, but does not represent the state of the data at any single point in time. This is because the data being backed up changed in the period of time between when the backup started and when it finished. For databases in particular, fuzzy backups are worthless.

Metadata

Not all information stored on the computer is stored in files. Accurately recovering a complete system from scratch requires keeping track of this non-file data too.

Manipulation of data and dataset optimisation

It is frequently useful or required to manipulate the data being backed up to optimize the backup process. These manipulations provide many benefits including improved backup speed, restore speed, data security, media usage and reduced bandwidth requirements.

Managing the backup process

It is important to understand that backup is a process. As long as new data is being created and changes are being made, backups will need to be updated. Individuals and organizations with anything from one computer to thousands (or even millions) of computer systems all have requirements for protecting data. While the scale is different, the objectives and limitations are essentially the same. Likewise, those who perform backups need to know to what extent they were successful, regardless of scale.

Objectives

Limitations

An effective backup scheme will take into consideration the limitations of the situation.

Implementation

Meeting the defined objectives in the face of the above limitations can be a difficult task. The tools and concepts below can make that task more achievable.

Measuring the process

To ensure that the backup scheme is working as expected, the process needs to include monitoring key factors and maintaining historical data.

Lore

Confusion

Due to a considerable overlap in technology, backups and backup systems are frequently confused with archives and fault-tolerant systems. Backups differ from archives in the sense that archives are the primary copy of data, usually put away for future use, while backups are a secondary copy of data, kept on hand to replace the original item. Backup systems differ from fault-tolerant systems in the sense that backup systems assume that a fault will cause a data loss event and fault-tolerant systems assume a fault will not .

Advice

Events

See also

References

  1. ^ English native speakers never say or write "she backups" or "he backuped" and instead always say and write the verb in two parts, in other words "(she) backs up" and "(he) backed up". Surprisingly, many even professional websites nevertheless confuse the noun and the verb and often misspell the verb in other situations, for example "to backup" ("will/must backup") instead of "to back up" etc. See also: American Heritage Dictionary entry for backup , American Heritage Dictionary entry for back up , Wiktionary entry for backup , Wiktionary entry for back up

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