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2019/11/18 13:52 1 Comment

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Backup Basics

Different kinds of Backup

FullA backup of all data. Most of the times combined with Incremental or Differential backups.YesFast
DailyChecks the date for files to backup. Only files that has been changes during the day are being backupped.NoNormal
IncrementalAn incremental backup will only back up files that have been changed since the last backup of any type. This provides the quickest means of backup, since it only makes copies of files that have not yet been backed up. YesSlow
DifferentialA cumulative backup of all changes made after the last full backup. The advantage to this is the quicker recovery time, requiring only a full backup and the latest differential backup to restore the system. The disadvantage is that for each day elapsed since the last full backup, more data needs to be backed up, especially if a majority of the data has been changed. NoNormal
Multilevel incrementalA more sophisticated incremental backup scheme involves multiple numbered backup levels. A full backup is level 0. A level n backup will back up everything since the most recent level n-1 backup. Assume a level 0 backup was taken on a Sunday. A level 1 backup taken on Monday would only include changes made since Sunday. A level 2 backup taken on Tuesday would only include changes made since Monday. A level 3 backup taken on Wednesday would only include changes made since Tuesday. If a level 2 backup was taken on Thursday, it would include all changes made since Monday because Monday was the most recent level n-1 backup. YesNormal
Reverse incrementalAn incremental backup of the changes made between two instances of a mirror is called a reverse incremental. By applying a reverse incremental to a mirror, the result will be a previous version of the mirror. NA NA
Synthetic full backupA synthetic backup is a form of an incremental backup that is possible when there is a separate computer that manages the backups. The backup server takes a typical incremental backup of the system in question and combines this data with the previous backups to generate a new synthetic backup. This new synthetic backup is indistinguishable from a normal full backup and shares all the advantages, such as faster restore times. YesFast
Incrementals foreverThis style is similar to the Synthetic backup concept. After an initial full backup, only incremental backups are sent to a centralized backup server. This server keeps track of all the incrementals and sends the proper data back to the server during restores. This can be implemented by sending each incremental directly to tape as it is taken and then refactoring the tapes as necessary. If enough disk space is available, an online mirror can be maintained along with previous incremental changes so that the current or older versions of the systems being backed up can be restored. YesSlow
Continuous data protectionThis model takes it a step further and instead of scheduling periodic backups, the system immediately logs every change on the host system. This is generally done by saving byte or block-level differences rather than file-level differences. It differs from simple disk mirroring in that it enables a roll-back of the log and thus restore of old image of data.NAFast

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backupbasics.txt · Last modified: 2019/11/18 12:21 (external edit)