VMware Distributed Resource Scheduler (DRS) is a VMware feature that optimizes the performance and resources of your vSphere cluster. Storage DRS was introduced in vSphere several releases ago, and it is still a key feature of vSphere 7.

Storage cluster configuration with Storage DRS (SDRS) in vSphere 7 allows you to balance virtual machine disk files (VMDK) between datastores in the datastore cluster.

In the same way as traditional DRS, where VMs are placed initially onto the healthiest host, the initial placement is manual with SDRS. After the VM is placed onto a datastore, the SDRS function keeps an eye on those datastores and makes sure none of them becomes completely filled.

If the utilization of the datastore rises above a predefined threshold, the DRS will issue a recommendation to move some VMDKs off this datastore and place them on a datastore with sufficient free space.

SDRS also monitors I/O latency and checks what has happened in the last 24 hours. There might have been a datastore with some heavy I/O over the past 24 h, which might mean the system won't move VMDKs onto it.

SDRS allows you to put a datastore into maintenance mode, allowing you to evacuate your VMDKs off to another datastore to enable decommissioning.

You can use VMFS or NFS-based datastores, but you can't combine VMFS with NFS in the same SDRS cluster. In this case, simply create separate SDRS clusters.

If you have some storage arrays that support hardware acceleration, you should not mix them with other arrays that don't have it. As a good practice, the datastore cluster should remain homogeneous.

How to create new datastore clusters ^

You'll need to log in via your vSphere web client. Select the relevant datacenter object. Right-click it and select Datacenter > Storage > New Datastore Cluster.

Create a new datastore cluster

Create a new datastore cluster

Then, on the next page, give it a meaningful name so you recognize which SDRS cluster you're working with. You can create several SDRS clusters within your datacenter.

Turn On Storage DRS checkbox

Turn On Storage DRS checkbox

Then, on the next page, you can choose between Fully Automated or No Automation (Manual mode). This is a one-or-the-other choice.

  • You have different granularity options available that allow you to override the cluster settings. This means that you can have cluster settings on fully automatic, but individual options can be set as needed.Space balance automation level—Shows what to do when there is a recommendation to correct a space load imbalance in a datastore cluster.
  • I/O balance automation level—Allows you to choose what happens when it generates recommendations for correcting an I/O load imbalance in a datastore cluster.
  • Rule enforcement automation level—Specifies SDRS behavior when it generates recommendations for correcting affinity rule violations in a datastore cluster. Affinity rules allow you to place different VMDKs on different datastores. Useful for Microsoft clustered applications, for example.
  • Policy enforcement automation level—Specifies SDRS behavior when it generates recommendations for correcting storage and VM policy violations in a datastore cluster.
  • VM evacuation automation level—Specifies SDRS behavior when it generates recommendations for VM evacuations from datastores in a datastore cluster.
Choose Fully Automated or Manual Mode

Choose Fully Automated or Manual Mode

The next page of the wizard presents you with Storage DRS Runtime Settings. You can set the different options for I/O where the I/O metrics are considered as a part of any SDRS recommendation or automated migration in this datastore cluster.

You can also set the I/O latency threshold and space threshold, such that you can set a minimum level of free space per datastore. Those settings allow you to migrate VMDKs off a datastore when the low space threshold kicks in.

Storage DRS runtime settings

Storage DRS runtime settings

The next page of the wizard allows you to select the cluster and hosts that will be part of the cluster.

Select clusters and hosts that will be part of the SDRS cluster

Select clusters and hosts that will be part of the SDRS cluster

The last page of the wizard shows us which datastores can be used. In our small lab case, we only have a local datastore, and as you can see, there is a warning telling us “Host connections missing.” This is because we only have a local datastore here, no shared datastores.

Host Connection Missing warning

Host Connection Missing warning

This concludes the creation of the datastore cluster in which we activated SDRS.

SDRS is an intelligent vCenter Server system that automatically and efficiently manages VMFS and NFS storage. It is very similar to DRS, which optimizes the performance and resources of your vSphere cluster.

Final words ^

VMware allows us to group different resources into clusters. With storage, we can create and use SDRS to balance VMDKs across different datastores and hosts.

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SDRS can run in automatic mode, but most admins will most likely privilege the manual mode so they have control and can assess when the system issues a recommendation.

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