SDRS does not recommend one or more datastores in the Cluster for initial placements even though enough free space available on these datastores

Products

• VMware vCenter Server

Issue/Introduction

• When VMs are moved to the SDRS cluster, it is always placed in the highly utilized datastore instead of selecting datastore with more free space.
• Datastores with more free space when compared to other Datastores in the Cluster are not recommended for initial placements.
• You might observe drastic difference in the space usage between the Datastores in the SDRS Cluster. For example, in a two datastore SDRS cluster, 1^st datastore is 50% used and the 2^nd datastore is used only 10%, still 1^st datastore is recommended for initial placements when new VMs are moved to this Cluster.
• Normal features of SDRS works fine, such as if any of the datastore hits the space threshold, SDRS moves the VM to other datastores without any issues.

Environment

vCenter Server 7.x

vCenter Server 8.x

Cause

This issue can be caused due to one or more VMs with high IO on certain datastores when compared to the VMs in other datastores in the SDRS Cluster.

Resolution

This is an expected behaviour as SDRS checks the space usage and the IO stats on the datastores before recommending the correct datastore for initial placements.

SDRS does not select the Datastore for the first recommendation if any VM on the same datastore has high IO when compared to the cumulative IO stats of all the VMs on other individual datastore in the Cluster.