Information AboutBackup |
| CATEGORIES ABOUT BACKUP | |
| computer storage | |
| data security | |
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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 computer to an operational state following a disaster (called Disaster Recovery ). The second is to restore small numbers of files after they have been accidentally deleted or corrupted. Why do I need to Backup my Files? . Retrieved on 2007-03-10 Backups are typically that ''last'' line of defense against data loss, and consequently the least granular and the least convenient to use. Backup – Your last line of defense . Retrieved on 2007-03-10 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 ever 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 would also like to have some 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 Archive s and Fault-tolerant System s. Backups differ from archives in the sense that archives are the ''primary copy'' of data and backups are a ''secondary copy'' of data. 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 . ; Unstructured : An unstructured repository may simply be a stack of floppy disks or CD-R media with minimal information about what was backed up and when. This is the easiest to implement, but probably the least likely to achieve a high level of recoverability. ; 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. Incremental Backup . Retrieved on 2007-03-10 ; Full + Differential : A full + differential backup differs from a full + incremental in that after the full backup is taken, each partial backup captures all files created or changed since the full backup, even though some may have been included in a previous partial backup. Its advantage is that a restore involves recovering only the last full backup and then overlaying it with the last differential backup. Differential Backup . Retrieved on 2007-03-10 ; 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. ; in that it enables a roll-back of the log and thus restore of old image of data. Storage media Regardless of the repository model that is used, the data has to be stored on some data storage medium somewhere. ; Magnetic Tape : Magnetic tape has long been the most commonly used medium for bulk data storage, backup, archiving, and interchange. Tape has typically had an order of magnitude better capacity/price ratio when compared to hard disk, but recently the ratios for tape and hard disk have become a lot closer.[http://www.storagesearch.com/engenio-art2.html Disk to Disk Backup versus Tape - War or Truce?] (2004-12-09). Retrieved on 2007-03-10 There are myriad formats, many of which are proprietary or specific to certain markets like mainframes or a particular brand of personal computer. Tape is a sequential access medium, so even though access times may be poor, the rate of continuously writing or reading data can actually be very fast. Some new tape drives are even faster than modern hard disks. |
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