To ensure efficient and reliable data protection in your virtual environment, Veeam Backup & Replication complements image-based backup with image-based replication. Replication is the process of copying a VM from its primary location (source host) to a destination location (redundant target host). Veeam Backup & Replication creates an exact copy of the VM (replica), registers it on the target host and maintains it in sync with the original VM.
Replication provides the best recovery time objective (RTO) values, as you actually have a copy of your VM in a ready-to-start state. That is why replication is commonly recommended for the most critical VMs (which run tier 1 applications) that need minimum RTOs. Veeam Backup & Replication provides means to perform both onsite replication for high availability (HA) scenarios and remote (offsite) replication for disaster recovery (DR) scenarios. To facilitate replication over WAN or slow connections, Veeam Backup & Replication optimizes traffic transmission — it filters out unnecessary data blocks (such as, duplicate data blocks, zero data blocks or blocks of swap files) and compresses replica traffic. Veeam Backup & Replication also allows you to apply network throttling rules to prevent replication jobs from consuming the entire bandwidth available in your environment.
Replication is a job-driven process with one replication job used to process one or more VMs. You can start the job manually every time you need to copy VM data or, if you want to run replication unattended, create a schedule to start the job automatically. Scheduling options for replication jobs are similar to those for backup jobs. For details, see Scheduling.
In many respects, replication of VMware VMs works similarly to forward incremental backup. During the first run of a replication job, Veeam Backup & Replication copies 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 uncompressed in their native format. All subsequent replication job runs are incremental (that is, Veeam Backup & Replication copies only those data blocks that have changed since the last replication cycle).
For every replica, Veeam Backup & Replication creates and maintains a configurable number of restore points. If the original VM fails for any reason, you can temporary or permanently fail over to a replica and thus restore critical services with minimum downtime. If the latest state of a replica is not usable (for example, if corrupted data was replicated from source to target), you can select previous restore point to fail over to. Veeam Backup & Replication utilizes VMware ESX snapshot capabilities to create and manage replica restore points. A new incremental run of the replication job takes a regular snapshot of a replica. Blocks of data that have changed since the last job run are written to the snapshot delta file and the snapshot delta file acts as a restore point.
VMware replica restore points are stored in a native VMware format next to replica virtual disk files, which allows Veeam Backup & Replication to accelerate failover operations. To restore a replica in the required state, there is no need to apply rollback files. Instead, Veeam Backup & Replication uses native VMware mechanism of reverting to a snapshot.
As well as for backup jobs, for replication jobs you can define a retention period. Veeam Backup & Replication will keep only the specified number of points, removing any snapshots that breach the retention policy. For details, see Retention Policy.
If the Veeam backup server becomes unavailable, you can fail over to any existing replica restore point without Veeam Backup & Replication (via vSphere Client or using a PowerCLI script).
You can define a retention period for replication jobs in the same way as backup jobs. Veeam Backup & Replication will keep only the specified number of points, removing any snapshots that breach the retention policy. For details, see Retention Policy.
Replicas include the following files:
●Full VM replica (a set of VM configuration files and virtual disks)
●Replica restore points (snapshot delta files)
●Replica metadata (.vbk files) used to store replica checksums. Veeam Backup & Replication uses this file to quickly detect changed blocks of data between two replica states. For details, see Changed Block Tracking.
The full VM replica along with its restore points is stored in a dedicated folder on the target datastore. Replica metadata files are located on a backup repository.