CBT-enabled VM having multi-writer disk(s) is not supported
Article ID: 382693
Updated On:
Products
Issue/Introduction
Powering ON a VM fails with the error.
Operation failed!
Task name Power On virtual machine
Target VMName
Status Cannot enable changed block tracking and multi-writer sharing at the same time.
Changing the sharing option from Multi-writer to Unspecified/No sharing fails.
Operation failed!
Task name Reconfigure virtual machine
Target VM Name
Status The operation is not supported on the object.
Environment
VMware vSphere ESXi
Cause
The multi-writer option in vSphere allows the VMFS-backed disks to be shared by multiple VM’s simultaneously.
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.
This is an unsupported configuration (CBT and Multi-writer): CBT and Multi-writer can never be configured simultaneously on VMs
Resolution
If the VM's configuration does not support multi-writer OR the VM is removed from an application cluster OR the cluster configuration is broken and you are unable to power ON the VM.
There are 2 ways to power ON the VM using such configuration -
1. Disable CBT using the Changed Block Tracking (CBT) on virtual machines KB
2. If you don't want to do Step-1 because it will interfere with the next backup; disable multi-writer from the VMX file thru CLI
3. Insert a # at the beginning of the scsi#:#.sharing parameter in the VMX file for all the disks.
scsi0:0.deviceType = "scsi-hardDisk"scsi0:0.fileName = "VMware.vmdk"
#scsi0:0.sharing = "multi-writer"sched.scsi0:0.shares = "normal"
You can verify that all the multi-writer lines have been commented out by searching the file using the grep command
Example output of how it should look after the lines have been prefixed with a hash.
[root@ESXi:/vmfs/volumes/5f4facab-########-####-############/VMName] cat VMName.vmx | grep -i multi#scsi1:0.sharing = "multi-writer"#scsi1:1.sharing = "multi-writer"#scsi1:2.sharing = "multi-writer"#scsi1:4.sharing = "multi-writer"#scsi1:5.sharing = "multi-writer"
You should be able to power ON the VM.
In some cases you may need to reload the vmx configuration for the changes to recognized by vSphere please see Reloading a vmx file without removing the virtual machine from inventory for more details on the reload process.
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