For legacy replicas, Veeam Backup & Replication uses an approach that is similar to reverse incremental backup.
During the first run of a replication job, Veeam Backup & Replication copies the VM running on the source host and creates its full replica on the target host. The replica is stored decompressed, in a native Hyper-V format.
All subsequent replication jobs are incremental. Veeam Backup & Replication copies only those data blocks that have changed since the last replication cycle. To keep track of changed data blocks for Hyper-V VMs, Veeam Backup & Replication uses its proprietary changed block tracking mechanism.
At every incremental job run, Veeam Backup & Replication “injects” changes into the replica to rebuild it to the most recent state of the source VM. It also creates a rollback file to store data blocks that were replaced when the full replica was rebuilt.
As a result, for every replicated VM, Veeam Backup & Replication produces a full replica and a chain of rollback files. The replica mirrors the latest state of the source VM, while rollback files serve as restore points. If you need to restore a replica to a particular point in time, Veeam Backup & Replication will apply the required rollback files to get you to that point in time.
Veeam Backup & Replication creates and maintains the following types of replica files:
- Full VM replica (a set of VM configuration files and virtual disks)
- VRB — replica rollback files
- VBK — file that stores hash data describing the current state of a VM replica on the target host
All files of a legacy replica are stored in a dedicated folder on the target volume.
Limitations for Legacy Replicas
The following limitations apply to the legacy replicas:
- Legacy replicas can use only the virtual infrastructure as a source of data. Replication from backup is not supported for legacy VM replicas.
- You cannot clone a legacy replication job that replicates a VM from the source Microsoft Hyper-V Server 2008 R2 host to the target Microsoft Hyper-V Server 2012 host or later using the Veeam Backup & Replication console or Veeam Backup Enterprise Manager web UI.