Incremental and Differential backups are the primary means by which ZCB reduces the size of backup runs after the Full Backup. Incremental and Differential backups are very similar, but have several key differences in how they function.
There are also some requirements that must be met for Incremental and Differential backups to perform their intended function.
A Differential backup will back up any data that has changed since the last Full Backup. Because they contain all changed data since the last Full Backup, Differential backups will start small but grow in size. Each one will be larger than the one before it, until you perform the next Full Backup. The rate of growth depends on the amount of data you change. For many, it is slow. For others, quite fast.
Performing a new Full Backup will reset the Differentials back to their smallest size.
To perform a full restore of all data, you will need the most recent Full Backup and the most recent Differential backup.
An Incremental Backup will back up any data that has changed since the last backup, be it Full, Differential, or Incremental.
This means that all Incremental Backups will be small in size, compared to a Full backup. There is no growth in file size over time, unlike Differential backups. The exact size of the backup depends entirely on how much data changes between backups.
A full restore of all data involving Incremental backups needs:
Incremental backups are generally much smaller in size than differential backups, but they can make the restore process slower over a period of time.
Differential backups, on other hand, offer a good tradeoff between "time to backup" and "time to restore".
To reap the benefits of both incremental and differential backups, you may combine both types in a single backup set. A backup set that mixes both incremental and differential backups may look like this: