VMware vSphere High Availability (HA) is a feature that helps to ensure the availability of virtual machines (VMs) in a vSphere environment. It does this by providing features such as host failure tolerance, application failover, and storage-level redundancy. In this article, we will discuss the details of VMware vSphere HA, its components, and how it works to ensure high availability for virtual machines.

Components of VMware vSphere HA:

1. Host Failure Tolerance (HFT): This feature allows VMs to continue running even if one or more hosts in the cluster fail. HFT uses a technique called “host isolation” to isolate the failed host and move the affected VMs to other hosts in the cluster.

2. Application Failover (AF): This feature allows applications to fail over to another host in the event of a failure. AF uses a heartbeat mechanism to detect when an application is no longer running on its original host and then fails it over to another host.

3. Storage-Level Redundancy (SLR): This feature provides redundancy at the storage level by using shared datastores and/or replication between datastores. SLR helps to ensure that data is available even in the event of a storage failure.

How VMware vSphere HA Works:

1. Host Failure Tolerance (HFT): When a host fails, HFT uses host isolation to move the affected VMs to other hosts in the cluster. The isolated host is then brought back online and the VMs are returned to their original hosts.

2. Application Failover (AF): When an application fails, AF fails it over to another host in the cluster. The failed application is then restarted on the new host.

3. Storage-Level Redundancy (SLR): In the event of a storage failure, SLR uses replication or shared datastores to ensure that data is available. If a VM’s data is stored on a failed storage device, SLR will replicate the data to another storage device and fail over the VM to a healthy host.

Proactive HA:

In vSphere 6.5, a new feature called Proactive HA was introduced. This feature allows for more advanced failure detection and response. With Proactive HA, hosts can be placed into maintenance mode or quarantine mode before a failure occurs, allowing for more proactive maintenance and reducing the risk of downtime.

Host Isolation Response:

In the event of a host failure, VMware vSphere HA uses a technique called “host isolation response” to isolate the failed host and move the affected VMs to other hosts in the cluster. This ensures that the VMs continue to run without interruption and reduces the risk of data loss.

Conclusion:

VMware vSphere HA is a powerful feature that helps to ensure the high availability of virtual machines in a vSphere environment. By providing features such as host failure tolerance, application failover, and storage-level redundancy, vSphere HA can help to minimize downtime and data loss in the event of a failure. With the addition of Proactive HA in vSphere 6.5, hosts can be placed into maintenance mode or quarantine mode before a failure occurs, allowing for more proactive maintenance and reducing the risk of downtime even further.