Full, incremental and differential backups
Seagate BlackArmor Backup can create full, incremental and differential backups.
A full backup contains all data at the moment of backup creation. It forms a base for further incremental or differential backup or is used as a standalone archive. A full backup has the shortest restore time compared to incremental or differential ones.
An incremental backup file only contains data changed since the last backup of any type (full, incremental, or differential one). Therefore, it is smaller and takes less time to create, but as it doesn’t contain all data; all the previous backups and the initial full backup are required for restoration.
Unlike an incremental backup, when every backup procedure creates the next file in a “chain”, a differential backup creates an independent file, containing all changes since the last full backup. Generally, a differential backup will be restored faster than an incremental one, as it does not have to process through a long chain of previous backups.
A standalone full backup might be an optimal solution if you often roll back the system to its initial state or if you do not like to manage multiple files. If you are interested in saving only the last data state to be able to restore it in case of system failure, consider the differential backup. It is particularly effective if your data changes tend to be few compared to the full data volume.
The same is true for incremental backup. These are most useful when you need frequent backups and the ability to roll back to a specific point in time. Having created a full backup once, if you then create an incremental backup each day of a month, you will get the same result as if you created full backups every day. Incremental images are considerably smaller than full or differential images.
Incremental or Differential?
The difference is typically that in an incremental backup, only the files changed or added since the last time the backup ran are added to the archive. With a differential backup, all the files changed or added since the initial full backup, are added to the archive. Thus, differential backups take longer to run than incremental backups. When restoring from an incremental backup, the program must copy the entire initial backup and then step through each of the previous backups to retrieve all the updated files. A differential backup, on the other hand, can be restored more quickly because the software must copy only the original backup and the most recent one.
An incremental or differential backup created after a disk is defragmented might be considerably larger than usual. This is because the defragmentation program changes file locations on the disk and the backups reflect these changes. Therefore, it is recommended that you re-create a full backup after disk defragmentation.
Select whether you want to create a full, incremental or differential backup. If you have not backed up the selected data yet, or the full archive is old and you want to create a new master backup file, choose full backup. Otherwise it is recommended that you create an incremental or differential backup. If you select the Full method, the Automatic consolidation step will be disabled. If you are adding a backup to the existing backup archive, the Full method will be unselectable.
You can set a backup policy for the backup task. Seagate BlackArmor Backup offers three types of backup policies:
Create full backups only.
Create full backups after a specified number of incremental backups.
Create full backups after a specified number of differential backups.
When the first backup on a schedule is executed, a full backup will be created. If you choose (2) or (3) by selecting the Create a new full backup after box, the next backups will be incremental (or differential) until the specified number of incremental (differential) backups is reached. After the selected number of incremental or differential backups is made, the next time a new full backup and a set of subsequent incremental (differential) backups will be created; this process will then continue until you decide to change it.
When the Remove old archives box is selected, creation of a new full backup in accordance with the specified backup policy results in deletion of the complete old backup chain – the old full backup and its subsequent incremental (or differential) backups regardless of the overall limitations you set on the archive at the Automatic consolidation step.
If you decide to keep old backups (by not selecting the Remove old archives box) and creation of a new full backup results in violation(s) of the limits set for automatic consolidation, the program will use the following algorithm:
If the actual number of backups exceeds the maximum number of backups, the program automatically consolidates the old full backup with the oldest incremental (differential) one to correct this quota violation.
If after correcting the number of backups limit violation there remains other quota violation(s), the program consolidates the oldest backup to correct the storage period of old backups limit violation (if possible - otherwise it deletes the old full backup).
If after correcting the storage period of old backups limit violation there remains the archive size limit violation, the program consolidates the old full backup with the oldest incremental (differential) one, then will repeat consolidation (if necessary and possible).
If after consolidating all the previous backups the archive size quota violation remains, the old backup archive will be deleted in order to correct the violation.
If the new full backup file size exceeds the archive size limit, the program will record a warning into the logs.