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Last updated: Mar 12, 2024

Difference between HA and DRS in VMware vSphere

VMware offers a number of hypervisors, which are all considered to be among the best options out there for anyone running VMs. With VMware hypervisors, you can run multiple virtual machines on a single host server. Also, you can have multiple hosts connected over a network, so you can migrate your VMs to and fro.

But, with the ability to migrate VMs from one host to another comes discrepancies such as downtimes during the migrations or workload imbalances caused by clusters on the server(s). Apparently, the last thing an IT professional or system admin would like to face is downtime. So, VMware clustering features like HA and DRS are there to help mitigate server-related issues in different ways.

VMware HA (High Availability) and DRS (Distributed Resource Scheduler) are meant for different conditions, which are clearly explained in this article.

VMware vSphere Clustering Features: HA and DRS

HA and DRS are clustering features of the VMware vSphere platform meant to come in handy on different occasions to mitigate host failures and VM data transfer errors. A vSphere cluster refers to two, three, or more ESXi hosts connected together over a network – sharing the same hardware resources such as memory, processor, and storage on the host system.

You can manage VMware vSphere clusters in vCenter and ESXi hosts included in a cluster are called “cluster nodes.” That said, there are two types of VMware vSphere clusters: High Availability (HA) and Distributed Resource Scheduler (DRS). To deploy these vSphere clustering features, the following conditions must be met.

  • You must have two or more ESXi hosts with the same configurations such as the same processor family (Intel or AMD), patch level, and ESXi version. However, it is advisable to use at least three ESXi hosts for more effectiveness.
  • You need high-speed network connections for all networks used: management network, vMotion network, and storage network. Also, you will need redundant network connections.
  • All clustered ESXi hosts must share the same datastore or have access to one particular datastore. You can use a Network Attached Storage (NAS), Storage Area Network (SAN), or VMware vSAN as the shared datastore.
  • Your connections should support NFS and iSCSI protocols for access to the data on the shared datastore that stores the VMs’ files.
  • Your installed ESXi host versions must be compatible with VMware vCenter Server.

Note: No quorum is needed for VMware vSphere cluster unlike in a Hyper-V Failover Cluster.

What is VMware HA?

VMware High Availability (HA) is a vSphere clustering feature that automatically restarts a virtual machine (VM) in case of failure (such as experiencing a failed ESXi host). This allows the VM and its connected applications to continue running provided they’re all in the same vSphere cluster. So, with VMware HA enabled, even if an ESXi host fails, the VMs on the host would be automatically on a healthy host so the end users will only experience a short downtime.

vSphere HA Requirements

To run vSphere HA in a clustered environment, your virtualization environment must meet the following requirements.

  • VMware vSphere Standard license
  • At least two ESXi hosts with the same configuration
  • The hosts must be using a shared datastore and utilize at least 4GB RAM per host.
  • High-speed network connections for all networks used and redundant physical network connections
  • A pingable gateway
  • Your ESXi host versions must be compatible with VMware vCenter Server

How does vSphere HA Work?

It simply checks your ESXi hosts looking out for failures; once a host failure is detected, vSphere HA will automatically migrate and register the VMs on the failed host to a healthy one in the same clustered environment, then restart the VMs. You can still access the VM files such as the VMX and VMDK files on the shared datastore – vSphere HA does not migrate the VM files.

Apparently, there will be some downtime during the migration process; the length of the downtime depends on the amount of time needed to restart the migrated VM(s) on another host. More so, VMware HA does not rely on the guest operating system installed on the VM. When vSphere detects a failed host, only the CPU, memory, and network components of the VMs deployed on the failed host are changed to that of the healthy host after the migration.

What is vSphere DRS?

Distributed Resource Scheduler, shortened as DRS, is a VMware vSphere cluster feature for host optimization and balancing. It balances the loads exerted by the VMs running in a cluster to ensure that there is no “overloaded” host, which could lead to downtime and performance issues.

If DRS sees an overloaded host or VM, it automatically moves the VM to another host (in the cluster) with enough free resources to handle the VM’s load; this ensures Quality of Service (QoS) within the cluster and promotes operations efficiency. vSphere DRS requires there is enough resources in your cluster environment.

VMware DRS Requirements

  • vSphere Enterprise or Enterprise Plus license
  • At least two ESXi hosts with the same configurations
  • A dedicated vMotion network
  • The hosts must be using a shared datastore – could be a SAN, NAS, or VMware vSAN
  • High-speed network connections for all networks used and redundant physical network connections
  • Your ESXi host versions must be compatible with VMware vCenter Server

How Does vSphere DRS Work?

vSphere DRS performs a load check for all ESXi hosts in a cluster every 5 minutes (you can adjust the timing interval). DRS checks mainly the RAM and CPU usage of VMs and hosts in a cluster; if it detects that a node is offline, or a VM/host resource usage is high in the cluster, it launches vMotion to migrate the overloaded VM(s) to another host without interrupting any ongoing process. VMware DRS resources check is carried out based on the configured policies.

What is a VMware Cluster?

A VMware cluster is an environment of multiple running ESXi servers. ESXi allows creating and running multiple VMs on a single server, but when you’ve got more than one ESXi server or host, you can form a cluster by connecting to vCenter. VMware vCenter allows you to run and manage multiple clusters. To form a VMware Cluster, you have to use the same server configuration for all the ESXi hosts you want to include in the cluster.

vSphere Cluster requirements

You must use the same server environment for all ESXi hosts in the cluster, most especially, the same CPU. If one of your hosts is using AMD processors, and the rest are built on Intel processors, only the hosts on Intel processors can be used in the same cluster.

Only when you have set up a VMware vSphere Cluster environment can you implement HA or DRS, or both at the same time.

Understanding the differences between VMware HA vs. DRS

When an ESXi host fails, a failover is initiated on that host by vSphere HA to migrate and restart the VMs on another healthy host. This is a first priority action to ensure minimal downtime; however, after HA migrates the VMs from the failed hosts to another one, the new host (where the VMs were migrated to) might become overloaded. This would take a toll on the performance of the VMs it houses - that’s where DRS can come in. VMware DRS will check the ESXi hosts in a cluster, determine the overloaded host, and take rapid action to balance load across all the hosts.

VMware vSphere HA and DRS are not competitive features, you can run both of them on your clustered environment. Each of them has a different function and won’t interfere with the other’ in fact, these two features complement each other.

Activating both HA and DRS will ensure constantly distributed load across your VMs, as well as ensure high availability (reduced downtime). You should enable these two features if you’re running VMs for production environments.

How to Configure HA and DRS in VMware?

vSphere HA

  • Log in to VMware vSphere Client and go to “cluster” in the Hosts and Clusters menu.
  • Right-click on the cluster you want to edit and select “Settings.”
  • Go to Configure 🡺 vSphere Availability 🡺 Edit 🡺 toggle the vSphere HA switch
  • Go to the Failures and Responses tab and activate Enable Host Monitoring.
  • You can manually edit the vSphere HA configurations in the Advanced Options tab.

Save your edits – click OK.

vSphere DRS?

  • In VMware vSphere Client, go to the clusters page, click on the “Configure” tab, further click on vSphere DRS in the Services pane, and click EDIT.
  • Toggle the vSphere DRS switch
  • Go to the “Automation” tab and choose between Fully and Partially automated options. Also set Migration Threshold.
  • Get into the “Additional Options” tab and configure VM Distribution, Scalable Shares, and CPU Over-Commitment.
  • Finally, tune the Distributed Power Management settings and make any further adjustments in the “Advanced options” tab.
  • Click OK to save and exit when done.

Comparition table VMware HA vs. DRS


vSphere HA

vSphere DRS


Automatically restarts failed VMs on a new healthy host in the cluster

Automatically balances load across ESXi hosts in a cluster based on resource utilization


vSphere Standard

vSphere Enterprise or Enterprise Plus

vMotion Network 

Not needed


vCenter Compatibility



Deployment Purpose

To eliminate or minimize downtime due to host failures

To promote efficiency and adequate utilization of resources in a cluster 

VMware Backup Solution

While HA and DRS can help to ensure the smooth operation of your VMs and applications, they do not offer any sort of redundancy or data backup. Hence, having a VMware backup solution is much advised.

A VMware backup solution will help to keep all your VM data backed up and saved in a safe haven for easy recovery in disaster situations. The DiskInternals VMFS Recovery software comes with a Disk Image creation function, which simply clones the hard drives that contain your VMware VMs’ data. You can easily recover the disk image at any time.

Using VMware HA and DRS Together

Using VMware High Availability (HA) and Distributed Resource Scheduler (DRS) together enhances the availability and efficiency of your virtual environment. VMware HA provides rapid recovery from outages by automatically restarting virtual machines (VMs) on other hosts if a server fails. DRS, on the other hand, optimizes VM performance by distributing them across hosts in a cluster based on resource availability and predefined rules.

When you combine VMware HA with DRS, you get a robust system that not only ensures your VMs are always running but also that they are running optimally. DRS can even respond proactively to avoid potential issues by moving VMs before a host becomes overloaded or encounters a problem, reducing the likelihood of VM failure and the need for HA intervention.

In this integrated setup:

  • HA monitors the health of physical servers: If a host fails, HA steps in to restart its VMs on other hosts within the resource pool, minimizing downtime.
  • DRS optimizes resource utilization: It continuously monitors resource usage across hosts and VMs, balancing loads to prevent any single host from becoming a bottleneck, which in turn helps in maintaining a more stable and reliable environment suitable for HA operations.
  • Enhanced coordination: When HA triggers a failover and restarts VMs on new hosts, DRS can immediately rebalance these VMs across the cluster to ensure optimal performance, preventing any one host from being overwhelmed post-failover.
  • Preventive actions: DRS can also take preemptive actions based on predictive data about host resource usage, moving VMs before a potential host failure occurs, which dovetails with HA's goal of minimizing service interruption.

Using VMware HA and DRS together thus provides a dual layer of protection and efficiency, ensuring not only that your applications remain available but also that they perform well, adapting dynamically to changing conditions in the virtual environment.


This article explains the two common vSphere cluster features and how you can implement them. You must understand how each of these features works, and follow the provided guide in setting them up. Running HA and DRS in one cluster is totally fine and recommended.


  • How to configure HA and drs in VMware?


    • Navigate to the cluster using the vSphere Client.
    • Select Configure.
    • In the Services section, choose vSphere DRS and then click Edit.
    • Check the boxes for Turn ON vSphere DRS and Turn on vSphere HA.
    • Click OK to apply the changes.
  • What is the difference between DRS and availability in vSphere?

    VMware HA safeguards applications operating within the resource pool that lack a failover alternative, guaranteeing uninterrupted availability of the virtual machine. Concurrently, VMware DRS allocates resources and evenly distributes workloads throughout the vSphere cluster, ensuring that every host and virtual machine is adequately resourced.

  • What is the difference between predictive DRS and proactive HA?

    • Focus: Predictive DRS focuses on balancing resources and optimizing performance based on predicted workload patterns, while Proactive HA focuses on maintaining availability by reacting to hardware health alerts before actual failures occur.
    • Action Trigger: Predictive DRS actions are triggered by anticipated resource demands and trends, whereas Proactive HA actions are triggered by hardware health alerts.
    • Objective: The primary objective of Predictive DRS is to ensure balanced resource utilization and optimal VM performance, while Proactive HA aims to prevent downtime due to imminent hardware issues.
    • Integration: Predictive DRS requires integration with vRealize Operations Manager, whereas Proactive HA requires integration with hardware vendors' monitoring solutions.
  • What is the difference between DRS and availability in vSphere?

    VMware HA safeguards applications within the resource pool that lack an alternate failover mechanism, thereby guaranteeing the VM's constant availability. Concurrently, VMware DRS administers resources and evenly distributes workloads throughout the vSphere cluster, ensuring sufficient resources for every host and virtual machine.

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