AskDefine | Define backup

Dictionary Definition



1 an accumulation caused by clogging or a stoppage; "a traffic backup on the main street"; "he discovered a backup in the toilet"
2 someone who takes the place of another (as when things get dangerous or difficult); "the star had a stand-in for dangerous scenes"; "we need extra employees for summer fill-ins" [syn: stand-in, substitute, relief, reliever, backup man, fill-in]
3 a subordinate musical part; provides background for more important parts [syn: accompaniment, musical accompaniment, support]
4 (computer science) a copy of a file or directory on a separate storage device; "he made a backup in case the original was accidentally damaged or erased" [syn: computer backup]
5 the act of providing approval and support; "his vigorous backing of the conservatives got him in trouble with progressives" [syn: backing, championship, patronage]

User Contributed Dictionary



From back up

Alternative spellings


  1. A reserve or substitute.
    If the goalkeeper is injured, we have a backup.
  2. A copy of a file or record, stored separately from the original, that can be used to recover the original if it is destroyed or damaged.
    After the power failure, we had to restore the database from backup.
  3. An accumulation of material that halts the flow or movement of something.
    The blockage caused a backup in the plumbing.



copy of file or record


  1. standby, reserve or extra
    I am only a backup player.
  2. That is intended as a backup.
    Make a backup copy of that file.


Usage notes

Back-up is an alternative spelling of backup. Both spellings see usage as noun or adjective. The verb back up is always spelled as two words and never with a hyphen.


standby, reserve or extra (1)
intended as backup (2)

Extensive Definition

In information technology, backup 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." 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. Backups are typically that last line of defense against data loss, and consequently the least granular and the least convenient to use.
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.
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 and backups are a secondary copy of data. Archives are the primary copy of the item, usually put away for future use, while backups are the secondary copy, 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.

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. ; Full + Incrementals : A Full + Incremental repository aims to make storing several copies of the source data more feasible. At first, a full backup (of all files) is taken. After that an incremental backup (of only the files that have changed since the previous full or incremental backup) can be taken. Restoring whole systems to a certain point in time would require locating the full backup taken previous to that time and all the incremental backups taken between that full backup and the particular point in time to which the system is supposed to be restored. This model offers a high level of security that something can be restored and can be used with removable media such as tapes and optical disks. The downside is dealing with a long series of incrementals and the high storage requirements. ; Mirror + Reverse Incrementals: A Mirror + Reverse Incrementals repository is similar to a Full + Incrementals repository. The difference is instead of an aging full backup followed by a series of incrementals, this model offers a mirror that reflects the system state as of the last backup and a history of reverse incrementals. One benefit of this is it only requires an initial full backup. Each incremental backup is immediately applied to the mirror and the files they replace are moved to a reverse incremental. This model is not suited to use removable media since every backup must be done in comparison to the mirror.

Storage media

Regardless of the repository model that is used, the data has to be stored on some data storage medium somewhere. ; Hard disk : The capacity/price ratio of hard disk has been rapidly improving for many years. This is making it more competitive with magnetic tape as a bulk storage medium. The main advantages of hard disk storage are low access times, availability, capacity and ease of use. External disks can be connected via local interfaces like SCSI, USB, FireWire, or eSATA, or via longer distance technologies like Ethernet, iSCSI, or Fibre Channel. Some disk-based backup systems, such as Virtual Tape Libraries, support data de-duplication which can dramatically reduce the amount of disk storage capacity consumed by daily and weekly backup data. ; Floppy disk : During the 1980s and early 1990s, many personal/home computer users associated backup mostly with copying floppy disks. The low data capacity of a floppy disk makes it an unpopular and obsolete choice today. ; Remote backup service : As broadband internet access becomes more widespread, remote backup services are gaining in popularity. Backing up via the internet to a remote location can protect against some worst-case scenarios such as fire, flood, earthquake or nuclear strike which would destroy any backups in the immediate vicinity along with everything else. A drawback to a remote backup service is that an internet connection is usually substantially slower than the speed of local data storage devices, so this can be a problem for people with large amounts of data. It also has the risk associated with putting control of personal or sensitive data in the hands of a third party.

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. ; Near-line : Near-line storage is typically less accessible and less expensive than on-line storage, but still useful for backup data storage. A good example would be a tape library with restore times ranging from seconds to a few minutes. A mechanical device is usually involved in moving media units from storage into a drive where the data can be read or written.; Off-site vault : To protect against a disaster or other site-specific problem, many people choose to send backup media to an off-site vault. The vault can be as simple as the System Administrator’s home office or as sophisticated as a disaster hardened, temperature controlled, high security bunker that has facilities for backup media storage.

Selection, extraction and manipulation of data

Selection and extraction of file data

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.

Selection and extraction of 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.
When attempting to understand the logistics of backing up open files, one must consider that the backup process could take several minutes to back up a large file such as a database. In order to back up a file that is in use, it is vital that the entire backup represent a single-moment snapshot of the file, rather than a simple copy of a read-through. This represents a challenge when backing up a file that is constantly changing. Either the database file must be locked to prevent changes, or a method must be implemented to ensure that the original snapshot is preserved long enough to be copied, all while changes are being preserved. Backing up a file while it is being changed, in a manner that causes the first part of the backup to represent data before changes occur to be combined with later parts of the backup after the change results in a corrupted file that is unusable, as most large files contain internal references between their various parts that must remain consistent throughout the file.

Selection and extraction of 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.; Boot sector : The boot sector can sometimes be recreated more easily than saving it. Still, it usually isn't a normal file and the system won't boot without it.; File metadata : Each file's permissions, owner, group, ACLs, and any other metadata need to be backed up for a restore to properly recreate the original environment.

Manipulation of data

It is frequently useful to manipulate the data being backed up to optimize the backup process. These manipulations can improve backup speed, restore speed, data security, and media usage.; De-duplication : When multiple similar systems are backed up to the same destination storage device, there exists the potential for much redundancy within the backed up data. For example, if 20 Windows workstations were backed up to the same data repository, they might share a common set of system files. The data repository only needs to store one copy of those files to be able to restore any one of those workstations. This technique can be applied at the file level or even on raw blocks of data, potentially resulting in a massive reduction in required storage space. Deduplication can occur on a server before any data moves to backup media, sometimes referred to as source/client side deduplication. This approach also reduces bandwidth required to send backup data to its target media. The process can also occur at the target storage device, sometimes referred to as inline or back-end deduplication; ; Encryption : High capacity removable storage media such as backup tapes present a data security risk if they are lost or stolen. Encrypting the data on these media can mitigate this problem, but presents new problems. First, encryption is a CPU intensive process that can slow down backup speeds. Second, once data has been encrypted, it can not be effectively compressed (although since redundant data makes cryptanalytic attacks easier many encryption routines compress the data as an integral part of the encryption process). Third, the security of the encrypted backups is only as effective as the security of the key management policy.

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.


; Recovery Time Objective (RTO) : The amount of time elapsed between disaster and restoration of business functions.


An effective backup scheme will take into consideration the limitations of the situation.; Performance impact : All backup schemes have some performance impact on the system being backed up, and such impact should be analyzed.; Network Bandwidth : Distributed backup systems can be impacted by limited network bandwidth.


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.; Authentication : Over the course of regular operations, the user accounts and/or system agents that perform the backups need to be authenticated at some level. The power to copy all data off of or onto a system requires unrestricted access. Using an authentication mechanism is a good way to prevent the backup scheme from being used for unauthorized activity.

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. ; Reporting : In larger configurations, reports are useful for monitoring media usage, device status, errors, vault coordination and other information about the backup process.; Validation : Many backup programs make use of checksums or hashes to validate that the data was accurately copied. These offer several advantages. First, they allow data integrity to be verified without reference to the original file: if the file as stored on the backup medium has the same checksum as the saved value, then it is very probably correct. Second, some backup programs can use checksums to avoid making redundant copies of files, to improve backup speed. This is particularly useful for the de-duplication process.



  • The more important the data that is stored on the computer the greater the need is for backing up this data.
  • A backup is only as useful as its associated restore strategy.
  • Storing the copy near the original is unwise, since many disasters such as fire, flood and electrical surges are likely to cause damage to the backup at the same time.
  • Automated backup and scheduling should be considered, as manual backups can be affected by human error.
  • Backups will fail for a wide variety of reasons. A verification or monitoring strategy is an important part of a successful backup plan.
  • It is good to store backed up archives in open/standard formats. This helps with recovery in the future when the software used to make the backup is obsolete. It also allows different software to be used.


  • In 1997, during a fire at the headquarters of Credit Lyonnais, a major bank in Paris, system administrators ran into the burning building to rescue backup tapes because they didn't have offsite copies. Crucial bank archives and computer data were lost.
  • Privacy Rights Clearinghouse has documented 16 instances of stolen or lost backup tapes (among major organizations) in 2005 & 2006. Affected organizations included Bank of America, Ameritrade, Citigroup, and Time Warner.
  • On 3 January 2008, an email server crashed at TeliaSonera, a major Nordic telecom company and internet service provider. It was subsequently discovered that the last serviceable backup set was from 15 December 2007. Three hundred thousand customer email accounts were affected.


backup in Bosnian: Backup
backup in Catalan: Còpia de seguretat
backup in Czech: Záloha (informatika)
backup in German: Datensicherung
backup in Spanish: Copia de seguridad
backup in Esperanto: Sekurkopio
backup in Basque: Segurtasun kopia
backup in French: Sauvegarde
backup in Croatian: Sigurnosna kopija
backup in Italian: Backup
backup in Hebrew: גיבוי
backup in Luxembourgish: Backup
backup in Dutch: Back-up
backup in Japanese: バックアップ
backup in Korean: 백업
backup in Polish: Kopia bezpieczeństwa
backup in Portuguese: Backup
backup in Russian: Резервное копирование
backup in Albanian: Back-up
backup in Slovak: Zálohovanie dát
backup in Finnish: Varmuuskopiointi
backup in Swedish: Säkerhetskopiering
backup in Chinese: 备份
backup in Persian: فرآیند پشتیبانی

Synonyms, Antonyms and Related Words

about-face, about-turn, advocate, agent, alter ego, alternate, alternative, amicus curiae, analogy, attorney, back track, back trail, backing, backing off, backing out, backing up, backup man, champion, change, changeling, comparison, copy, counterfeit, deputy, double, dummy, equal, equivalent, ersatz, exchange, executive officer, exponent, fake, figurehead, fill-in, ghost, ghostwriter, imitation, lieutenant, locum, locum tenens, makeshift, metaphor, metonymy, mock, next best thing, paranymph, personnel, phony, pinch, pinch hitter, pleader, procurator, provisional, proxy, relief, replacement, representative, reserve, reserves, reversal, reverse, reversing, reversion, right-about, right-about-face, ringer, second in command, second string, secondary, sign, spare, spares, stand-in, stopgap, sub, substituent, substitute, substitution, succedaneum, superseder, supplanter, surrogate, swingaround, symbol, synecdoche, temporary, tentative, third string, token, turnabout, turnaround, understudy, utility, utility man, utility player, vicar, vicar general, vicarious, vice, vice-president, vice-regent, vicegerent, volte-face
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