Veeam Backup & Replication is built for virtual environments. It operates at the virtualization layer and uses an image-based approach for VM replication.
Veeam Backup & Replication does not install agent software inside the VM guest OS to retrieve VM data. To replicate VMs, it leverages VMware vSphere snapshot capabilities. When you replicate a VM, Veeam Backup & Replication requests VMware vSphere to create a VM snapshot. The VM snapshot can be thought of as a cohesive point-in-time copy of a VM including its configuration, OS, applications, associated data, system state and so on. Veeam Backup & Replication uses this point-in-time copy as a source of data for replication.
In many respects, replication works similarly to forward incremental backup. During the first replication cycle, Veeam Backup & Replication copies data of the original VM running on the source host, and creates its full replica on the target host. Unlike backup files, replica virtual disks are stored decompressed in their native format. All subsequent replication cycles are incremental. Veeam Backup & Replication copies only those data blocks that have changed since the last replication job session. To keep track of changed data blocks, Veeam Backup & Replication uses different approaches. For more information, see Changed Block Tracking
Veeam Backup & Replication lets you perform onsite replication for high availability (HA) scenarios and remote (offsite) replication for disaster recovery (DR) scenarios. To facilitate replication over the WAN or slow connections, Veeam Backup & Replication optimizes traffic transmission. It filters out unnecessary data blocks such as duplicate data blocks, zero data blocks, blocks of swap files and blocks of excluded VM guest OS files, and compresses replica traffic. Veeam Backup & Replication also allows you to use WAN accelerators and apply network throttling rules to prevent replication jobs from consuming the entire network bandwidth.
In Veeam Backup & Replication, replication is a job-driven process. To perform replication, you need to configure replication jobs. A replication job is a configuration unit of the replication activity. The replication job defines when, what, how and where to replicate. One replication job can be used to process one or several VMs. You can instruct Veeam Backup & Replication to run jobs automatically by schedule or start them manually.
Limitations for Replication
Replication has the following limitations:
- Due to VMware vSphere limitations, if you change the size of VM disks on the source VM, Veeam Backup & Replication deletes all available restore points (represented as VM snapshots) on the VM replica during the next replication job session. For more information, see this VMware KB article.
- If you assign the role of a backup proxy to a VM, you should not add this VM to the list of processed VMs in a job that uses this backup proxy. Such configuration may result in degraded job performance. Veeam Backup & Replication will assign this backup proxy to process other VMs in the job first, and processing of this VM itself will be put on hold. Veeam Backup & Replication will report the following message in the job statistics: VM is a backup proxy, waiting for it to stop processing tasks. The job will start processing this VM only after the backup proxy deployed on the VM finishes its tasks.
- If you use tags to categorize virtual infrastructure objects, check limitations for VM tags. For more information, see VM Tags.
- Due to Microsoft limitations, you cannot use Microsoft Azure Active Directory credentials to perform application-aware processing on VMs running Microsoft Windows 10.
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