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Engineering LibreTexts

12-F.18: Backup and Restore in Linux

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    2.3 Given a scenario, create, modify, and redirect files.
    2.6 Given a scenario, back up, restore, and compress files.

    System Backup

    In information technology, a backup, or data backup is a copy of computer data taken and stored elsewhere so that it may be used to restore the original after a data loss event. The verb form, referring to the process of doing so, is "back up," whereas the noun and adjective form is "backup." Backups can be used to recover data after its loss from data deletion or corruption, or to recover data from an earlier time. Backups provide a simple form of disaster recovery; however 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.

    A backup system contains at least one copy of all data considered worth saving. The data storage requirements can be large. An information repository model may be used to provide structure to this storage. There are different types of data storage devices used for copying backups of data that is already in secondary storage onto archive files. There are also different ways these devices can be arranged to provide geographic dispersion, data security, and portability.

    Data is selected, extracted, and manipulated for storage. The process can include methods for dealing with live data, including open files, as well as compression, encryption, and de-duplication. Additional techniques apply to enterprise client-server backup. Backup schemes may include dry runs that validate the reliability of the data being backed up. There are limitations and human factors involved in any backup scheme.

    Full Backup

    A full backup is when every single file and folder in the system is backed up. A full backup takes longer and requires more space than other types of backups but the process of restoring lost data from backup is much faster.

    Incremental Backup

    Subsequent backups only store changes that were made since the previous backup. The process of restoring lost data from backup is longer but the backup process is much quicker.

    Differential Backup

    The initial backup is full and subsequent backups only store changes made to files since the last backup. This type of backup requires more storage space than incremental backup does, but it also allows for a faster restore time.

    Mirror Backup

    An exact copy is made of the source data. The advantage of mirror backup is that there is no storing of old, obsolete files. When obsolete files are deleted, they disappear from the mirror backup as well when the system backs up. The downside to mirror backup is that if files are accidentally deleted, they can be lost from the backup as well if the deletion isn’t discovered before the next scheduled backup.

    Difference Between Incremental Backup and Differential Backup

    1. Incremental Backup

    Incremental backup only preserves the data that has been changed from the last full backup or incremental backup. This type of backup uses less storage and can do backup and recovery quickly. The data in this type of backup contains redundancy as recovery includes last full backup and all the incremental backups.

    1. Differential Backup

    Differential backup only preserves data change from the last full backup. This type of backup uses more memory as it saves all the data changes since last full backup. It contains less redundant data and recovery is easy but the time needed for creating backup is high.

    Difference between Backup and Snapshot

    1. Backup

      Backup generally suggests the duplicate of your data. When a backup is initiated, it generates copies of your files, comprising files pertaining to your website and mailboxes. These copies are conventionally kept in a different location than the original content, thus making them ideal for disaster rehabilitation. Backups are the mechanism that could take minutes, hours, or days to complete, depending on the data. This conveys that the data at the end of the backup may not be compatible with the data at the time when the backup initiated. Backups are planned to be stored for long periods of time and, if they are stored off server, they can be used to restore servers after a server failure.
    2. Snapshot

      Snapshot refers to an instantaneous “picture” of your server’s file system at a certain period of time. This picture apprehends the entire file system as it was when the snapshot was taken. When a snapshot is accustomed to restore the server, the server will revert to exactly how it was at the time of the snapshot. Snapshots are designed for short term storage. When space departs, new snapshots eventually overwrite older ones. For this reason, snapshots are usually only good if you want to revert to a recent version of your server.

    Difference Between Backup and Snapshot:

    Backup Snapshot
    Backup can be stored in another location, same server, or even the same drive in this case. Snapshots can be stored only in the same location where original data is present.
    Backup may have differences based on when the backup started and ended. Snapshot is a “picture” of your server at present period of time.
    It is a long term process and might take a lot of time to complete the procedure. It is a short term process and takes much less time, as compared to backup, to complete the procedure.
    Backup comprises only the file system. Snapshots comprises different types of systems like the files, software, and settings of that type.
    Backup takes a long time to copy data. Snapshot takes much less time to copy the data.
    In case of SQL server, backup is a paid service. A person can use this service to automatically backup the most recent data every night. In case of SQL server, snapshot is a free feature that is used to manually create duplicate images of the servers. One can easily generate them at any time.
    Backup is not a backup unless the data exists in several distinct locations. Backups should be easily and quickly restored. Backups should be verifiable. Snapshot by itself is not a backup. But it can be used as an essential part of the backup process. Snapshot is used as a part of the data movement process to a backup file. It is removed when the backup job is completed.

    Adapted from:
    "Backup" by Multiple Contributors, Wikipedia is licensed under CC BY-SA 3.0
    "Difference between Backup and Snapshot" by sommprasad, Geeks for Geeks is licensed under CC BY-SA 4.0
    "Difference between incremental backup and differential backup" by kapilsparshi, Geeks for Geeks is licensed under CC BY-SA 4.0

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