High Availability in Hyper-V: How does it work?

High Availability (HA) in Hyper-V refers to the capability of maintaining consistent and reliable access to virtual machines (VMs) even in the face of hardware failures, network issues, or other disruptions. Microsoft’s Hyper-V provides several features and technologies to implement high availability, ensuring that critical workloads remain accessible and operational. The primary technologies for achieving high availability in Hyper-V include Failover Clustering, Hyper-V Replica, and Shared Nothing Live Migration.

Clustering

High Availability in Hyper-V is often implemented using Failover Clustering. A failover cluster is a group of independent servers that work together to increase the availability of applications and services. All Hyper-V hosts (nodes) in the cluster are connected to shared storage, typically through Storage Area Network (SAN) or Scale-Out File Server (SOFS). Nodes in the cluster communicate with each other through a dedicated network known as the cluster heartbeat. This network is separate from the regular data network and is crucial for detecting node failures.

Another strategy used in Hyper-V is the quorum. A quorum is the mechanism by which the cluster determines which nodes are active and should continue operating. Quorum configurations help prevent “split-brain” scenarios where multiple nodes believe they are the primary node.

The cluster storage is based on CSVs (Cluster Shared Volumes). Cluster Shared Volumes allow multiple nodes in the cluster to read and write to the same storage simultaneously. This is crucial for maintaining shared access to VM files on all nodes.

Clusters then enable VMs to move from node to node, which is called Live Migration. Failover Clustering enables Live Migration, allowing VMs to be moved between nodes with minimal downtime. This technology is particularly useful for planned maintenance or load balancing.

In the event of a hardware or software failure on one node, the VMs running on that node can be automatically “failed over” to another healthy node in the cluster. In a nutshell, this is how Hyper-V achieves high availability with a minimal risk of downtime.

Hyper-V Replica

Hyper-V Replica, on the other hand, uses asynchronous replication. Hyper-V Replica provides a kind of a disaster recovery solution by asynchronously replicating VMs from one Hyper-V host (primary site) to another (replica site).
The Hyper-V Replica Broker is a module that facilitates the coordination of replication and failover processes. It helps manage replication traffic and provides a single entry point for initiating failover.
Hyper-V Replica creates recovery points at regular intervals, allowing administrators to roll back VMs to a previous state in case of data corruption or other issues. Hyper-V Replica then allows for planned and unplanned failovers. A planned failover is a maintenance operation, whereas unplanned failovers occur when a node has a technical failure.

Shared Nothing Architecture and Live Migration

Shared Nothing Live Migration is a technology that allows administrators to move VMs between Hyper-V hosts without shared storage. Each host maintains its own storage. In Live Migration without downtime, on the other hand, VMs can be moved between hosts with minimal downtime, providing flexibility for load balancing, hardware maintenance, or addressing resource constraints.
Shared Nothing Live Migration eliminates the need for shared storage, making it a more straightforward option for environments without a SAN or shared storage infrastructure. By not requiring shared storage, this technology also reduces the investment required by SMB to deploy Hyper-V clusters.

Summary

High Availability in Hyper-V is achieved through a combination of Failover Clustering, Hyper-V Replica, and Shared Nothing Live Migration. These technologies provide a range of options for maintaining continuous access to virtualized workloads, whether through automatic failover within a cluster, asynchronous replication for disaster recovery, or seamless migration between hosts. Implementing high availability in Hyper-V is a critical component of ensuring business continuity and minimizing disruptions in virtualized environments.

BackupChain: The Best Backup Solution for Hyper-V Virtual Machines, Servers, and Clusters

BackupChain in an all-in-one backup solution for Windows that contains all physical backup features you will ever need, plus a complete virtual machine backup toolset for Hyper-V, VMware, VirtualBox and other hypervisors. BackupChain can be used to create a live backup of each VM from the host as a local backup or as cloud backup. Apart from backing up VMs, BackupChain offers a wide range of host-level backup features, as well as Granular Backup and Granular Restore to speed up the recovery process.

BackupChain only needs to be installed on the host and each license includes unlimited live virtual machine backup on these main platforms:

• Hyper-V Backup on Windows Server 2022 – 2008 as well as Windows 11 – 8 hosts
• VMware Backup on all Windows platforms
• VirtualBox Backup on all Windows platforms
• Cloud Backup for Virtual Machines