Enabling Fault Tolerance on a virtual machine with an extended disk size fails with the error: Unsupported virtual machine configuration for Fault Tolerance

Products

• VMware vCenter Server

Issue/Introduction

Symptoms:

• Enabling Fault Tolerance (FT) on a virtual machine with an extended disk size fails
• Cannot enable FT on a virtual machine with an extended disk size
• You see an error similar to:

Unsupported virtual machine configuration for Fault Tolerance.
The Unused Disk blocks of the Virtual machine's disk have not been scrubbed on the filesystem. This is needed to support features like fault tolerance.

Environment

VMware vCenter Server 4.1.x
VMware vCenter Server 5.1.x
VMware vCenter Server 4.0.x
VMware vCenter Server 5.0.x
VMware vCenter Server 6.0.x

Cause

This issue occurs because FT cannot be enabled on a powered-on virtual machine that has thick formatted, lazy-zeroed disks.

Resolution

This is a known issue affecting VMware vCenter Server 4.0, 4.1, 5.0, and 5.1.

This issue is resolved in vCenter Server 6.0. For more information, see VMware vSphere 6.0 Release Notes

 

Additional Information

For more information, see the VMware Availability Guide for your version of ESX.

Perform these steps to extend disk on a FT enabled virtual machine:
 

1. Power off the FT virtual machine.
2. Disable FT on the Primary virtual machine. For more information on disabling FT, see Disabling or turning Off VMware FT (1008026).
3. Extend the virtual disk. For more information on increasing the virtual disk, see Increasing the size of a virtual disk (1004047).
   
   Note: When extending the vmdk using vmkfstools, use -d eagerzeroedthick to keep the disk-type for FT intact.
    
4. Enable Fault Tolerance on the Primary virtual machine.
   
   Note: When enabling Fault Tolerance again, this causes the vmdk to become EagerZeroedThick. If the virtual disk is large, turning on FT can take some time to complete.
    
5. Power on the FT virtual machine.

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Increasing the size of a virtual disk
Disabling or turning Off VMware FT