Backup chain transform helps reduce disk space required for storing backups on a backup repository. This is functionality additional to the synthetic full backups.
With backup chain transform enabled, Veeam Backup & Replication transforms the active backup chain (the latest full backup file and subsequent incremental backup files, VBK and VIBs) into reverse incremental backup files, VRBs. As the result of the transform operation, you will have only one synthetic full backup file instead of two full backup files — a regular full backup and synthetic full backup.
Veeam Backup & Replication applies short-term retention policy to the transformed chains without delays — Veeam Backup & Replication just deletes a VRB backup file. However, the transform operation takes more time than creating a periodic synthetic full backup. The transform operation produces heavy load on the backup repository. Make sure you properly plan the use of backup repository resources when you schedule backup jobs.
Veeam Backup & Replication transforms only the active backup chain. All backup files that precede the active backup chain stay intact.
How Backup Chain Transform Works
For example, you have configured a backup job to perform daily forward incremental backups and scheduled synthetic full backups on Thursday. Additionally, you have selected to transform the incremental backup chain into the reverse incremental backup chain. The backup job starts on Sunday. In this case, Veeam Backup & Replication performs backup in the following way:
- On Sunday, Veeam Backup & Replication creates a full backup file.
- Monday through Wednesday, Veeam Backup & Replication creates increments and adds them to the backup chain.
- On Thursday, Veeam Backup & Replication creates a new increment and then transforms the backup chain in the following way:
- Veeam Backup & Replication injects the Monday increment into the Sunday full backup. Modified blocks are pulled out and saved as a reverse incremental file. As a result, you have Monday full backup and Sunday reverse increment.
- Veeam Backup & Replication repeats the process for Tuesday, Wednesday and Thursday increments. As a result, you have the synthetic full backup created on Thursday and a set of reverse increments for Sunday through Wednesday.
- When you run the backup job next time, Veeam Backup & Replication adds a new increment to the backup chain. The synthetic full backup will be used as a starting point.
Retention Policy for Mixed Backup Chains
To maintain the necessary number of restore points in mixed backup chains (backup chains that contain reverse incremental and forward incremental backup files), Veeam Backup & Replication deletes an outdated reverse incremental backup file when the job adds a new forward incremental backup file to the chain.