Hyper-V Backup and Replication: What is the Best?

Hyper-V backup and Hyper-V replication are important strategies for Hyper-V protection. However, there are some critical differences between the two that one must understand in order to set up an efficient Hyper-V backup strategy. While both methods provide some form of duplication for virtual machines but the goal of each strategy is quite different.

Is Hyper-V Replication the same as Hyper-V Backup?

Hyper-V replication is basically the act of performing a VM copy from one server to another. Replicating moves everything from physical host A to B. If you use Hyper-V Replica, this process will occur at the sector-level every 15 mins. It sounds like a great idea but there are drawbacks to this type of a “backup”, namely, it isn’t a real backup. This type of a copy of a VM, and especially the Hyper-V Replica kind, isn’t a crash-consistent or application consistent grade of a Hyper-V backup. A Hyper-V Backup is a much more advanced backup mechanism but also requires more work to be performed.

Is Hyper-V Backup better than a Hyper-V Replica?

Hyper-V Backup is a process where the host specifically tells the VM to prepare for live backup. This involves passing a signal inside the VM into its VSS aware services, such as SQL Server, the Windows operating system itself, Exchange Server, etc. so that all services that need to prepare have a chance to do so. The services then flush out any pending write blocks so that their on-disk data structures are in a guaranteed consistent state. Once all services are done and happy, the signal is passed back and the backup at the host-level can begin.
As you can see, the Hyper-V backup requires a lot of overhead. This is not the same as Hyper-V Replica, which simply moves blocks from A to B, and not even always in their right sequence, without the services inside the VM being notified. If a connection to a replica breaks, the result is usually catastrophic. You can also not just take a replica and power it up just like that. There is no guarantee that the replication is up-to-date at random points in time.
A Hyper-V Backup is hence way superior to Hyper-V Replica. It’s a copy of the VM taken at a very specific point in time. It’s a crash consistent and application consistent copy so it’s guaranteed to be in a good state when you use it. When the backup is complete, you know what you have. But there is an overhead involved in getting the Hyper-V backup to start.
Hyper-V Replica is a clever mechanism that you can use to copy VMs over very slow connections to another site. This works but has several drawbacks one has to be aware of. It’s a process that usually isn’t monitored well. It often stops working without IT admins noticing. Only when the replica is needed do IT admins realize that the replication had quietly stopped working months earlier, leaving them with no backup to restore from.

Can Hyper-V Backup be used as Replication?

Yes, but not in very short intervals. Using BackupChain you can use the Hyper-V Backup mechanism to produce a 1:1 copy of a VM and place it on a separate host or multiple hosts. The advantages are many: BackupChain offers very good monitoring and error logging. If anything goes wrong, you will be notified and you can spot the source of the error in the logs immediately. Having a Hyper-V Backup grade copy of the VM is always preferable, as described in the previous section in more detail, so the quality of the replication is much better if it originates from a Hyper-V backup.
In addition, Hyper-V backup offers another critical advantage: The ability to go back in time and restore much older versions of the VM. Hence, for a complete Hyper-V backup strategy it’s not enough to use replication. Replication only protects against sudden hardware failures of the main host. Anything beyond needs to be protected with appropriate Hyper-V backup strategies.
To implement Hyper-V backup and replication, we recommend using BackupChain.