How does Hyper-V Replica work and why is it important?
Hyper-V Replica is a disaster recovery feature that creates and maintains copies of virtual machines. The process of creating a replica involves the use of a primary host and a secondary host. When a replica is created, the VSS writer (a mechanism for creating application-consistent backups) creates a snapshot of the virtual machine on the primary host. The Replica function then copies the snapshot to the secondary host. That way, the organization has a standby server containing copies of its virtual machines, which are ready to be used at a moment's notice.
One of the most important things about the Hyper-V Replica feature is that it is designed solely as a disaster recovery feature and not a resiliency feature. If the primary server were to fail, Hyper-V does not automatically fail the virtual machines over to the replicas (for that, you would use failover clustering). Instead, Hyper-V Replica is a mechanism that allows virtual machine recovery to be easily delivered after a storage failure or other type of disaster.
It is worth noting that the replication process does not occur in real time; instead, it is asynchronous and is based on log shipping. This process occurs at five-minute intervals and is not configurable.
Creating Hyper-V replicas does not require that the primary host and the secondary host have identical hardware, but the secondary host must meet some minimal standards. Specifically, the secondary server must have enough memory, storage space and processing power to host the replicated virtual machines. And although it's not always an absolute requirement, the secondary server should ideally contain the same type of processor as the primary host to avoid compatibility problems.
This was first published in October 2012