A datastore cluster is a collection of datastores with shared resources and a shared management interface. Datastore clusters are to datastores what clusters are to ESXi hosts. After you create a datastore cluster, you can use vSphere Storage DRS to manage storage resources.

vSphere datastore clusters group similar datastores into a pool of storage resources. When vSphere Storage DRS is enabled on a datastore cluster, vSphere automates the process of initial virtual machine file placement and balances storage resources across the cluster to avoid bottlenecks. vSphere Storage DRS considers datastore space usage and I/O load when making migration recommendations.

When you add a datastore to a datastore cluster, the datastore's resources become part of the datastore cluster's resources. The following resource management capabilities are also available for each datastore cluster.

Capability

Description

Space utilization load balancing

You can set a threshold for space use. When space use on a datastore exceeds the threshold, vSphere Storage DRS generates recommendations or performs migrations with vSphere Storage vMotion to balance space use across the datastore cluster.

I/O latency load balancing

You can configure the I/O latency threshold to avoid bottlenecks. When I/O latency on a datastore exceeds the threshold, vSphere Storage DRS generates recommendations or performs vSphere Storage vMotion migrations to help alleviate high I/O load.

Anti-affinity rules

You can configure anti-affinity rules for virtual machine disks to ensure that the virtual disks of a virtual machine are kept on different datastores. By default, all virtual disks for a virtual machine are placed on the same datastore.

You can enable vSphere Storage I/O Control or vSphere Storage DRS for a datastore cluster. You can enable the two features separately, even though vSphere Storage I/O control is enabled by default when you enable vSphere Storage DRS. 

vSphere Storage DRS Background Information

vSphere Storage DRS supports automating the management of datastores based on latency and storage utilization. When configuring vSphere Storage DRS, verify that all datastores use the same version of VMFS and are on the same storage subsystem. Because vSphere Storage vMotion performs the migration of the virtual machines, confirm that all prerequisites are met.

vSphere Storage DRS provides a way of balancing usage and IOPS among datastores in a storage cluster:

  • Initial placement of virtual machines is based on storage capacity.

  • vSphere Storage DRS uses vSphere Storage vMotion to migrate virtual machines based on storage capacity.

  • vSphere Storage DRS uses vSphere Storage vMotion to migrate virtual machines based on I/O latency.

  • You can configure vSphere Storage DRS to run in either manual mode or in fully automated mode.

vSphere Storage I/O Control and vSphere Storage DRS manage latency differently.  

  • vSphere Storage I/O Control distributes the resources based on virtual disk share value after a latency threshold is reached.

  • vSphere Storage DRS measures latency over a period of time. If the latency threshold of vSphere Storage DRS is met in that time frame, vSphere Storage DRS migrates virtual machines to balance latency across the datastores that are part of the cluster.

When making a vSphere Storage design decision, consider these points:

  • Use vSphere Storage DRS where possible.

  • vSphere Storage DRS provides a way of balancing usage and IOPS among datastores in a storage cluster:

    • Initial placement of virtual machines is based on storage capacity.

    • vSphere Storage vMotion is used to migrate virtual machines based on storage capacity.

    • vSphere Storage vMotion is used to migrate virtual machines based on I/O latency.

    • vSphere Storage DRS can be configured in either manual or fully automated modes