By default, the initial backup performed for a resource is a full backup, and all subsequent backups are incremental backups. If a resource has been backed up for many times, and then all of its generated backups are deleted, and the resource is backed up again, the system will also perform a full backup for the resource.
- The initial full backup covers only the used capacity of a disk. If a 100 GB disk contains 40 GB data, the initial backup consumes 40 GB backup space.
- Subsequent incremental backup backs up data changed since the last backup. If 5 GB data changed since the last backup, only the 5 GB changed data will be backed up.
CBR allows you to use any backup, no matter it is a full or incremental one, to restore the full data of a resource. By virtue of this, manual or automatic deletion of a backup will not affect the restoration function.
Suppose server X has backups A, B, and C (in time sequence) and every backup involves data changes. If backup B is deleted, you can still use backup A or C to restore data.
In extreme cases, the size of a backup is the same as the disk size. The used capacity in a full backup and the changed capacity in an incremental backup are calculated based on the data block change in a disk, not by calculating the file change in the operating system. The size of a full backup cannot be evaluated based on the file capacity in the operating system, and the size of an incremental backup cannot be evaluated based on the file size change.