How to Clone a Virtual Machine When Source VM Has Disks Too Large for any Storage

Products

• VMware vCenter Server

Issue/Introduction

When attempting to clone a virtual machine (VM) using vSphere Client, the operation may fail if any virtual disks in the source VM are larger than the available space in the target datastore, even if those disks are not intended to be part of the final cloned VM.

Environment

- VMware vSphere 6.x and later
- vCenter Server
- ESXi hosts

- The "Clone to Virtual Machine" wizard prevents proceeding at the storage selection step
- Error message "Select a valid destination storage" appears
- Unable to reach the disk customization step where unwanted disks could be removed

Cause

The vSphere cloning process validates available storage space before allowing disk customization. This validation checks space requirements for all virtual disks, regardless of whether they will be included in the final clone.

Resolution

Two methods are available to work around this limitation:

Method 1: ESXi Command Line (No VM Downtime Required)

1. Note the current VM's configuration details:
   1. Take screenshots or document all VM settings
   2. Record the source datastore path for the drives intended to be cloned
   3. Note the target datastore path
      
      
2. Create a new VM in the destination datastore:
   1. Configure settings to match the source VM
   2. Do not create any virtual disks
      
      
3. Enable SSH on the ESXi host if not already enabled
   • Reference KB 312060 for SSH enablement steps
     
     
4. Connect to the ESXi host via SSH
   
   
5. List available datastores:
   • esxcli storage filesystem list
6. Use vmkfstools to clone only the desired virtual disk:
   1. Reference KB 343140 for specific vmkfstools commands
   2. Clone the C: drive to the new VM's location

Method 2: vCenter Server UI (Requires VM Downtime)

1. Document current virtual disk locations:
   1. Right-click VM > Edit Settings...
   2. Note paths for all virtual disks
   3. Ensure no snapshots exist
      
      
2. Remove large disks during maintenance window:
   1. Power off the VM
   2. Edit VM settings
   3. For each unwanted disk:
      • Click the three vertical dots next to the disk
      • Select "Remove device" (NOT "Remove device and delete files")
   4. Click OK
      
      
3. Perform clone operation normally
   
   
4. Reattach original disks to source VM:
   1. Edit source VM settings
   2. Click "ADD NEW DEVICE"
   3. Select "Existing Hard Disk"
   4. Navigate to original disk locations
   5. Add each disk back
   6. Power on VM

Additional Information

- Method 1 requires SSH access and command line experience
- Method 2 requires planned downtime
- As a rough rule of thumb, estimate maintenance window duration based on the time it takes to backup the disks being copied
- Double estimated time to account for complications
- Consider testing process on non-production VM first