Multiple storage vMotion tasks are initiated by SDRS for a single virtual machine, despite "Keep VMDKs together" being enabled

Products

• VMware vCenter Server

Issue/Introduction

• Storage DRS (SDRS) is enabled in fully automated mode
• after a single SDRS run there are multiple Storage vMotion tasks triggered for the same virtual machine (VM), despite the option "keep VMDKs together" having been enabled
• The VM has multple virtual disks (VMDKs) attached
• The attached VDMKs have delta files (aka snapshots)

Environment

• VMware vCenter Server 7.0.x / 8.0.x
• VMware vSphere ESXi 7.0.x / 8.0.x

Cause

• For VMs with multiple disks attached, where these disks have delta files (like the ones used for VM snapshots), every single disk chain will  be treated by SDRS as a separate entity, whereas VMs without delta files and VMs with a single disk only are being handled as a complete single entity.
• Therefore SDRS generates multiple recommendations within the same run, and - as the placement for each recommendation will be handled separately - will trigger multiple Storage vMotion tasks.

 

Resolution

• The option "Keep VMDKs together" will be taken into account when the recommendations are being made, therefore the resulting Storage vMotion tasks should not lead to the virtual machines disks being separated.
• However, the only way to fully prevent prevent SRDS from triggering multiple Storage vMotion tasks for a single VM is to get rid of the delta files, meaning to either consolidate the existing snapshots (when the current state of the VM should be kept) or to remove the snapshots (when the VM should be kept in a pre-snapshot state).

Additional Information

for more information about the "Keep VMDKs together" option, see https://knowledge.broadcom.com/external/article/373883