Quick rollback helps you significantly reduce the failback time. You can use quick rollback if you fail back from a VM replica to the original VM in the original location.
During failback, Veeam Backup & Replication calculates differences between disks of the original VM and disks of the VM replica. With the quick rollback option enabled, Veeam Backup & Replication compares only those disk sectors that have changed during the VM replica was in the Failover state instead of comparing entire disks. To get information about the changed disk sectors, Veeam Backup & Replication uses VMware vSphere Changed Block Tracking (CBT).
As a result of enabling quick rollback, difference calculation becomes much faster. After the differences are calculated, Veeam Backup & Replication performs failback in a regular way: transport changed blocks to the original VM, powers off the VM replica and synchronizes the original VM with the VM replica once again.
Requirements for Quick Rollback
To perform quick rollback, make sure that the following requirements are met:
- You fail back to the original VM in the original location.
- Do not use quick rollback if the problem occurred at the VM hardware level, storage level or due to a power loss.
Use quick rollback if you fail back to the original VM that had a problem at the guest OS level — for example, there was an application error or a user accidentally deleted a file on the original VM guest OS.
- CBT must be enabled for the original VM.
Limitations for Quick Rollback
The following limitations apply to quick rollback:
- Due to changes in VMware vSphere 7.0 and newer, the replica failback operation forces digest recalculation for both source and target VMs. That is why the Quick rollback option is ignored for ESXi hosts starting from version 7.0.
- During the first replication job session after failback with quick rollback, CBT on the original VM is reset. Due to that Veeam Backup & Replication will read data of the entire VM.