What Is DRS (Distributed Resource Scheduler) VMware

what is drs vmware

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There is so much talk about what is DRS VMware. Distributed Resource Scheduler is a technology that drives your virtual machine pleased. DRS frequently monitors your cluster utilization and ensures that your VMs will get their resources the most effective way.

Once you know what DRS VMware is, you will be able to reap the benefits of the virtualization process. DRS uses VMware vMotion to migrate virtual machines between ESXi hosts based on balancing algorithms and sensitivity.

To make it simple: DRS is accountable for maintaining your cluster proportional, so the utilization of the ESXi hosts is identical.

DRS also operates closely with resource management, ensuring particular resources for your virtual machines. DRS assesses many parameters that are estimated continuously for optimum performance and arrangement.

Those variables are:

  • destination host resource capability
  • resource reservations
  • datastore connectivity
  • actual resource demand from virtual machines

You can have a massive virtual machine that is not doing anything for a significant amount of time, but it will allocate all assigned resources.

DRS might even decide that another host will be more appropriate for such VM in such a case. You might migrate the VM to another ESXi host based on your automation level (Manual, Partially Automated, or Fully Automated).

DRS – Distributed Resource Scheduler functionality

VMware DRS runs within the VMware vCenter server to automatically balance the memory load of all virtual machines in the cluster.

DRS intelligently allocates resources and can automatically handle workload migration (with VMotion) or assign migrations based on administrator-defined rules. Using resource pools that combine multiple household resources into one, DRS enables the optimal distribution of virtual machine workloads based on business needs and changing priorities.

DRS migrates VMs based on CPU availability and usage, and memory resources. When faced with an increased VM load, DRS evaluates its priority over resource allocation rules and redistributes VMs to target application capacity with the highest priority.

DRS increases productivity by allowing an administrator to monitor many resources. DRS also reduces maintenance time. When the physical server is put into maintenance mode, the DRS automatically migrates all VMs to other servers. Enable DRS cluster to load balancing on the same host.

Requirements for DRS

The VMware DRS functionality requirements are as follows:

  • License name: VMware Enterprise Plus
  • Multiple ESXi hosts: At least two hosts is the minimum requirement, but VMware recommends at least three hosts for the workflow
  • Shared storage: the cluster have to contain SAN so that all hosts in the group can access all VM data repositories
  • Processor: Processors must be from the same manufacturer in the cluster so that there is no mixing of Intel with AMD. Interfering with the CPU architecture is not allowed because when a VM migrates live from one host to another, the destination CPU needs to be able to understand the exact instructions executed on the source host
  • Networking: There must be a dedicated network setup for migration between hosts

How to configure VMware DRS

  • Go to the main HA-Cluster in the Hosts & Clusters section. Next, click the Configure tab, then the vSphere DRS menu
  • Select the EDIT button from the right of the vSphere DRS is Turned ON setting
  • Turn on the vSphere DRS slider in the new pop-up window to turn green
  • Set the level of automation. There are three options available:
  1. Fully automated: DRS will settle which ESXi host will initially power the VM and move the VMs dictated by its algorithm to balance the cluster. The fully automated option is Set and Forget mode and is recommended for most configurations
    1. Partially Automated: No additional automated balancing will occur after the DRS decides which host to power the VM. DRS is recommending potential balancing actions in this mode, which the user must agree to before any action occurs
    2. Manual: DRS will only recommend including VM if it is a good move to maintain cluster balance. Manual mode requires the user always to accept any suggestions manually
  • The migration threshold is how DRS will transfer the virtual machines to keep the cluster balanced, whether it’s “aggressively” or “smoothly”. There are five levels from conservative to aggressive. The intermediate level is recommended and set by default. Yet, if VMs are moved frequently, adjusting to a more conservative level may be relevant
  • Click OK in order to save and apply the settings and the configuration is complete

VMware DRS features

Beyond the traditional DRS that balances CPU and memory resources across the cluster, there are even more DRS features:

  • DRS Storage (SDRS): Balances the use of data storage across data warehouses. It also examines capacity and performance metrics.
  • Predictable DRS: combines the power of vSphere 6.5+ and vROPS 6.4+ to shift workloads before proactive resource imbalances occur.
  • Elastic DRS: In AWS VMware Cloud, Elastic DRS dynamically expands and reduces your cluster by adding and removing ESXi hosts as required.

At the very heart of all types of DRS is an algorithm that pays attention to performance metrics and then moves things around to achieve optimal configuration.

Like vMotion, DRS has seen significant improvements in vSphere 6.5. One of these improvements was a change in algorithm that began to consider network usage for host performance.

How VMware vMotion and VMware DRS work simultaneously

vMotion lets things flow smoothly in a vSphere environment, and DRS decides how to move items around to deliver the best performance and proper outcome. When DRS must move something, it simply uses vMotion! Although these are entirely different technologies, they complement each other nicely.

Although vMotion and DRS may be entirely different technologies, they are perfect together. However, you can have vMotion without DRS, but you can not have DRS without vMotion. Hence the confusion because they work so closely together.

These features ensure the optimal performance of your VMware vSphere environment and allow you to move the workload around without affecting your applications and users as you see appropriate. vMotion and DRS have come a very long way due to the fact that their initial releases were numerous years ago and are sure to continue to evolve.

VMware vSphere clusters can automatically migrate virtual machines running on a destination host resources to enable DRS cluster. VMware virtual machines use one ESXi host resources as a virtual machine placement. A particular host is reserved for one particular VM. vSphere hosts and all the VMs power management for the virtualized environment to the idle consumed memory.


VMware Distributed Resource Scheduler constantly monitors your vSphere cluster and ensures that your VMs get the resources they require most efficiently.

VMware Distributed Resource Scheduler (DRS) checks the performance of your VMs and makes decisions about which host cluster a VM will migrate to. If it is in automatic mode, the VMs are automatically moved to other hosts.

We at VMware-ESXi.com wanted to start putting down definitions, such as DRS, for new folks starting with VMware virtualization technologies. That’s why this post is about the purpose of what is VMware DRS. We hope that it helped you figure out the basic concept.