Backup Snapshot removal for a VM with Zerto Replication is stuck at 0%

Products

• VMware vCenter Server

Issue/Introduction

• Backup Snapshot removal task on the affected VM stays running for hours without progressing usually stuck at 0%.
• Other operations on the VM fail with Another task is already in progress.

• VMs frequently enter a hung state and only recover after the VM process or world ID is killed at the ESXi command line.

• In /vmfs/volumes/<datastore>/<vm-folder>/vmware.log for the affected VM, you see entries similar to:

YYYY-MM-DDTHH:MM:SS Er(02) vcpu-0 - zdriverFilterC-#2-zsimple_pool_finish:64: Not all items were freed! 3413 out of 8192 missing.

Environment

VMware vSphere ESXi 8.x

Cause

A periodic timer callback coincide with the Zerto filter being finalized as a disk is closed during snapshot removal. 

Resolution

Engage Zerto Replication team for further assistance.