On hot-expand of non-shared disks, VMs on vsanDatastore lose SCSI-3 Persistent Reservations (SCSI-3 PR) on all attached disks

Products

• VMware vSAN 7.x
• VMware vSAN 8.x

Issue/Introduction

This KB describes a known limitation of virtual disk management where VMs are configured with SCSI-3 PR and stored on vsanDatastore.

Symptoms:
After hot-expanding a non-shared disk (increasing disk size while VM is powered-on), any virtual hard disk attached to a VM with SCSI-3 PR configured will lose its reservations. This will result in issues and reservations will have to be manually reconfigured.

 

Environment

VMware vSAN 7.0.x

VMware vSAN 8.0.x

Cause

Following hot-expansion of any disk attached to a VM, the VM is stunned and the vscsi devices destroyed and recreated, this results in the the persistent reservations being released - this is expected behavior with the current code implemented for vSAN-backed vmdk disks.

Resolution

Improvements have been implemented that will avoid this behavior will be included in a future release of ESXi so that non-shared disks can be hot-expanded without causing reservations on shared-disks to be removed.

Hot-expansion of shared-disks using SCSI-3 PR remains unsupported.

 

Workaround:
If non-shared disks need to be hot-expanded then reservations to all shared-disks will need to be re-applied.