Powering on the virtual machine fails with the error: Thin/TBZ disks cannot be opened in multiwriter mode
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Powering on the virtual machine fails with the error: Thin/TBZ disks cannot be opened in multiwriter mode

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Article ID: 311233

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Updated On:

Products

VMware vCenter Server VMware vSphere ESXi

Issue/Introduction

Symptoms:
  • Powering on the virtual machine fails.
  • You see the error:

    Reason: Thin/TBZ disks cannot be opened in multiwriter mode..
    Cannot open the disk '/vmfs/volumes/xxxxxxxx-xxxxx-xxxxxxxxxxxxxxx/Windows Server 2008/VM.vmdk' or one of the snapshot disks it depends on.
    VMware ESX cannot open the virtual disk, "/vmfs/volumes/xxxxxxxx-xxxxx-xxxx-xxxxxxxxxxx/Windows Server 2008/VM.vmdk" for clustering. Please verify that the virtual disk was created using the 'thick' option.
     
  • Cannot open Thin/TBZ disks in a multiwriter mode.
  • VMware ESX cannot open the virtual disk.

 

 



Environment

VMware vSphere ESXi 6.x
VMware vSphere ESXi 7.x
VMware vSphere ESXi 8.x

 

Cause

This issue occurs if the disk is not in a compatible format for multiwriter mode.
 
This issue most commonly occurs in configurations where an eagerzeroedthick virtual disk is shared across multiple virtual machines and is extended using the vSphere Client. When the disk is extended using the vSphere Client, it becomes lazyzeroedthick as the extended portion of the disk is LazyZeroed.
 

Resolution

This is an expected behavior, where the format of a virtual disk in multiwriter mode is changed to an unsupported format. For more information about the requirements of virtual disks in multiwriter mode, see Enabling or disabling simultaneous write protection provided by VMFS using the multi-writer flag.

To confirm the issue, verify the virtual disk format. To check the disk format, see Determining if a VMDK is zeroedthick or eagerzeroedthick.

To prevent this issue from re-occurring, ensure that virtual disks in multiwriter configurations are not converted to the lazyzeroedthick format. To use disks in multiwriter mode, the format must be Thick Provision Eager Zeroed.

(Note : vSphere Client default behavior is to create a lazy zeroed disk).

To extend a virtual disk in a multiwriter configuration, extend the virtual disk by running the vmkfstools -X command from the ESXi/ESX host command line. This ensures that the virtual disk format stays in the correct eagerzeroedthick format.

For example, to extend the size of the virtual disk to 60 GB:

# vmkfstools -X 60G -d eagerzeroedthick /vmfs/volumes/Datastore_name/virtual_Machine_folder/virtualmachinedisk.vmdk


Notes:

  • In the preceding vmkfstools -X example, 60 GB is the size that you want the disk file to be, is not the size by which you want to extend the disk file.
  • VMware recommends that you perform this operation outside of production, as it writes to the disk and takes significant time to complete.
  • For virtual machines that are running Microsoft Cluster Service (MSCS), ensure the disks containing the guest Operating System is not connected to a SCSI controller that is engaged in bus-sharing.
  • For NFS workaround please do refer to this document Attempts to enable the multi-writer virtual disk option on an NFS datastore fail  .


To fix the broken VMDK, one of the following two methods could be used:

  1. Storage vMotion to change the disk format. For more information, see the Migrate a Virtual Machine to New Storage section in the vCenter Server and Host Management guide.
  2. clone the disk using following command:
    # vmkfstools -i old.vmdk new.vmdk -d eagerzeroedthick

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