VMs with vVOLs based virtual disks takes long time to power on with CBT enabled

Products

• VMware vSphere ESXi

Issue/Introduction

Symptoms:

• VMs with vVOLs based virtual disks takes a long time to power on with CBT enabled.
• In the vmware.log, you see entries similar to:2017-11-02T06:43:48.366Z| vcpu-0| I125: 2335513:VVOLLIB : VVolLib_UnsharedChunksVVol:6216: Successful

2017-11-02T06:43:48.449Z| vcpu-0| I125: 2335513:VVOLLIB : VVolLibCopyBitmapResult:1666: Bitmap array size 1024
2017-11-02T06:43:48.509Z| vcpu-0| I125: 2335513:VVOLLIB : VVolLib_UnsharedChunksVVol:6216: Successful
2017-11-02T06:43:48.628Z| vcpu-0| I125: 2335513:VVOLLIB : VVolLibCopyBitmapResult:1666: Bitmap array size 1024
2017-11-02T06:43:48.685Z| vcpu-0| I125: 2335513:VVOLLIB : VVolLib_UnsharedChunksVVol:6216: Successful
2017-11-02T06:43:48.764Z| vcpu-0| I125: 2335513:VVOLLIB : VVolLibCopyBitmapResult:1666: Bitmap array size 1024

• CBT is enabled on the VM.

Environment

VMware vSphere ESXi 6.0

Cause

This issue occurs due to bottleneck with VVolLibCopyBitmapResult, that is building the map and taking to long per block.
CBT needs to get all allocated block to build up a bitmap during initialization.

Resolution

This is a known issue affecting vSphere 6.0.
Currently, there is no resolution.




Workaround:

To workaround the issue, disable CBT on the VM. For more information, see Enabling or disabling Changed Block Tracking (CBT) on virtual machines.