Backup granularity depends on business needs and required RTO/RPO. Based on granularity, backups can be categorized as full, cumulative, and incremental. Most organizations use a combination of these three backup types to meet their backup and recovery requirements.

Full backup is a backup of the complete data on the production volumes at acertain point in time. A full backup copy is created by copying the data on the production volumes to a secondary storage device. Incremental backup copies the data that has changed since the last full or incremental backup, which-ever has occurred more recently. This is much faster (because the volume of data backed up is restricted to changed data), but it takes longer to restore. Cumulative (or differential) backup copies the data that has changed since thelast full backup. This method takes longer than incremental backup but is faster to restore.

Synthetic (or constructed) full backup is another type of backup that is used inimplementations where the production volume resources cannot be exclusively reserved for a backup process for extended periods to perform a full backup. It is usually created from the most recent full backup and all the incremental backups performed after that full backup. A synthetic full backup enables a full backup copy to be created offline without disrupting the I/O operation on the production volume. This also frees up network resources from the backup process, making them available for other production uses.

Figure: Backup granularity level