Snapshot based incremental backup of Virtual Machine runs long behaving like a full backup.

Products

• VMware vSphere ESXi
• VMware vCenter Server

Issue/Introduction

Daily incremental backups of the VM runs for several hours similar to a full backup workflow. VMs with large sized disks (>10TB) can days to finish often missing the next schedule. 

VM is runs on the snapshot for long resulting in snapshot delete/consolidation running longer than expected.

Cause

Change Block Tracking is not enabled on one or more disks.

Changed Block Tracking (CBT) is a feature that identifies blocks of data that have changed or in use. It enables incremental backups to identify changes from the last previous backup, writing only changed or in-use blocks.

In the absence of CBT being enabled, incremental backup workflow has no ability to identify changed blocks resulting in full backup.

Resolution

Enabled Change Block Tracking on the virtual disks. Follow the steps outlined in Enabling or disabling Changed Block Tracking (CBT) on virtual machines to know how. 

Additional Information

In some cases even a Change Block Track enabled virtual machines can get into such state due to tracking failure of corruption. In such cases please reset the change block tracking following Resetting Changed Block Tracking for VMware vSphere virtual machines. Refer Changed Block Tracking (CBT) on virtual machines additional information.