Backup

In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is 'back up' (a phrasal verb), whereas the noun and adjective form is 'backup'. In information technology, a backup, or data backup, or the process of backing up, refers to the copying into an archive file of computer data that is already in secondary storage—so that it may be used to restore the original after a data loss event. The verb form is 'back up' (a phrasal verb), whereas the noun and adjective form is 'backup'. Backups are primarily to recover data after its loss from data deletion or corruption, and secondarily to recover data from an earlier time, based on a user-defined data retention policy. Though backups represent a simple form of disaster recovery and should be part of any disaster recovery plan, backups by themselves should not be considered a complete disaster recovery plan. One reason for this is that not all backup systems are able to reconstitute a computer system or other complex configuration such as a computer cluster, active directory server, or database server by simply restoring data from a backup. Since a backup system contains at least one copy of all data considered worth saving, the data storage requirements can be significant. Organizing this storage space and managing the backup process can be a complicated undertaking. An information repository model may be used to provide structure to the storage. Nowadays, 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 are sent to their storage locations, they are 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. Every backup scheme should include dry runs that validate the reliability of the data being backed up. It is important to recognize the limitations and human factors involved in any backup scheme. This article focuses on features found even in personal backup applications, as opposed to features found only in enterprise client-server backup applications. It also assumes at least a random access index to the secondary storage data to be backed up, and therefore does not discuss the decades-old practice of pure tape-to-tape copying. Any backup strategy starts with a concept of an information repository, 'a secondary storage space for data'. The backup data needs to be stored, so part of the model is the backup rotation scheme. The repository must have some kind of method behind it; the method could be as simple as a sheet of paper with a list of all backup media (DVDs, etc.) and the dates they were produced. A more sophisticated method could include a computerized index, catalog, or relational database. Different backup methods have different advantages: An incremental backup stores data changed since a reference point in time. Duplicate copies of unchanged data aren't copied. Typically a full (usually non-image) backup of all files is made on one occasion (or at infrequent intervals), serving as the reference point for an incremental repository. After that, a number of incremental backups are made after successive time periods. Restores begins with the last full backup and then apply the incrementals. Some backup systems can create a synthetic full backup from a series of incrementals, thus providing the equivalent of frequently doing a full backup. This, when done to modify a single archive file, speeds restores of recent versions of files even for personal backup applications. It should not be confused with a technique for creating a second archive file from a first, which is a capability of enterprise client-server backup applications. True Continuous Data Protection (CDP), allowing restoring data to any point in time, 'is the gold standard—the most comprehensive and advanced data protection. But 'near CDP' technologies can deliver enough protection for many companies with less complexity and cost. For example, snapshots can provide a reasonable near-CDP-level of protection for file shares, letting users directly access data on the file share at regular intervals—say, every half hour or 15 minutes. That's certainly a higher level of protection than tape-based or disk-based nightly backups and may be all you need.' Because 'near-CDP does this at pre-set time intervals', it is essentially incremental backup initiated—separately for each source machine—by timer instead of script.