Vmware DRS (Distributed Resource Scheduler)

Vmware DRS (Distributed Resource Scheduler)

Configuring vSphere DRS for VMware

What and Why

Since ESX/ESXi servers share resources with many virtual machines (VMs), if you have several ESX/ESXi severs as part of a cluster, there’s a general challenge to ensure resources are kept at optimal levels as each ESX server takes on new VMs.  To make sure resource management happens automatically and efficiently, it’s important to configure a cluster with the VMware Distributed Resource Scheduler (DRS).  DRS will not only automatically place a new VM to an ESX server that has available resources, ensuring other servers don’t become overloaded, but it will also move existing VMs to less utilized servers.  The configuration is straightforward and can have a huge impact on the performance and ease of management on the cluster.


Before diving into the procedure for turning on DRS, we first need to outline some requirements:

Make sure your version of vSphere supports DRS (it would be Enterprise or Enterprise+).

It’s important to have shared storage and that all ESX/ESXi servers can access it.

DRS uses vMotion to move VMs from one ESX host to another, so this will need to be enabled as part of your cluster.

The Steps

From the vSphere Web Client, click on ‘vCenter’ and then click on ‘Clusters’ to see the clusters available in your environment.  At this point I’m assuming you have an existing cluster to enable DRS, but if you need to create a cluster first, there is an option labeled ‘Turn ON vSphere DRS’ during the set-up process.

Click on an existing cluster and then click on the ‘Manage’ tab.  You’ll notice that you’re already viewing the ‘vSphere DRS’ settings under the ‘Services’ section.  If not, click on ‘vSphere DRS.’  You should be able to see that DRS is turned off (as shown by the red rectangle in the next screenshot).  On the same screen, click on ‘Edit’ to modify the cluster’s settings.

While you’re at the edit screen, click the checkbox titled ‘Turn ON vSphere DRS.’  Before clicking on ‘OK,’ take a look at the ‘DRS Automation’ options as shown in the screenshot below.

The ‘DRS Automation’ option has three values that will adjust how DRS will act when deciding which VMs are migrated from one server to another.  The options are:

Manual – DRS will display recommendations to move VMs, but will not actually move them to another server without manual action from the administrator.  This is useful for determining what impact placement or migration may have on the environment.

Partially Automated – DRS will automatically place new VMs that are first powered-on, but will only make recommendations for existing VMs.  This is a good option to ensure that balancing occurs as more VMs are added to the cluster, but without moving any existing VMs, which could cause performance issues.

Fully Automated – DRS will automatically place new VMs, as well as automatically migrating existing VMs to balance resources.  This is common for very large enterprises in which migrating an existing VM will have little impact, and the environment is too large for an administrator to manually move VMs.

If you’re testing the impact of DRS on a non-production environment (which I hope you are), select Fully Automated to see how DRS will respond in your environment.  If you’re still determining the full impact, I recommend starting with Manual orPartially Automated to get a feel for the recommendations that DRS will make.  Once the automation level is set, click on ‘OK’ to be taken back to the Manage screen.  Believe it or not, that’s it!  DRS has now been enabled.

Checking DRS

Now that you’ve enabled DRS, let’s take a look at its status.  Click on the ‘Summary’ tab to see the chart titled ‘vSphere DRS Balance level. ‘ In the screenshot, I drew a red rectangle around the Summary chart.  If you selected Fully Automated, as new VMs come online and start to use resources, this chart will adjust to indicate at what level the ESX servers are being utilized and how they’re managing the load.

Final Thoughts

With DRS now enabled on your cluster, you can sit back and enjoy life as vSphere takes care of resource management.  To continue down your DRS journey, I recommend reading Tuning the DRS Migration Threshold on the VMware blogs.  Keeping the DRS migration threshold as conservative will prevent VM migration from occurring unless there’s a major resource conflict, while setting the threshold to aggressive will allow VMs to migrate to keep resources optimal.  Most administrators choose a level somewhere in between, so it’s up to you to test this out (and please don’t test changes on production servers) to choose the best settings for your environment.

Thanks For Reading!!! All the Best…Smiley Happy

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‎07-22-2015 01:26 AM
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