How to Recreate a Missing Virtual Machine Disk Descriptor File VMDK?

A VMDK descriptor file is a critical component of VMware virtual machines, containing essential metadata about the virtual disk structure. When this file goes missing while the main flat data file remains intact, your VM becomes inaccessible. Common causes include accidental deletion, storage migration errors, or file system corruption.

VMDK File Structure

A VMDK consists of two main components:

• The descriptor file (small text file with .vmdk extension).
• The flat file (large binary file containing actual disk data, named filename-flat.vmdk).

The descriptor file contains:

• Disk geometry specifications;
• Hardware version;
• Disk type (flat/sparse/monolithic);
• Access permissions;
• Extended metadata.

Method 1: Manual Recreation

Create a new text file with vmdk extension containing:

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# Disk DescriptorFile

version=1

encoding=”UTF-8″

CID=fffffffe

parentCID=ffffffff

isNativeSnapshot=”no”

createType=”vmfs”

# Extent description

RW [size in sectors] VMFS “[datastore path to flat file]” 0

ddb.adapterType = “lsilogic”

ddb.geometry.cylinders = “[number]”

ddb.geometry.heads = “255”

ddb.geometry.sectors = “63”

ddb.virtualHWVersion = “14”

Replace the placeholders with actual values ​​from your environment and you will be able to recover vmdk from flat file without any problem.

Method 2: Using VMware Tools

Use vmkfstools to recreate the descriptor:

bash

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vmkfstools -I “[path to flat file]”

vmkfstools -r /vmfs/volumes/datastore/vm/disk-flat.vmdk /vmfs/volumes/datastore/vm/disk.vmdk

Verify with:

bash

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vmkfstools -v 10 -D “[path to new descriptor]”

Method 3: Recovery from Backup

1. Locate backup descriptor files in backup repositories.
2. Compare timestamps with flat file.
3. Copy descriptor file to original location.
4. Verify file permissions match VMware requirements.
5. Test VM startup.

Preventive Measures

To effectively protect VMDK files and prevent descriptor file loss, organizations should implement a comprehensive backup strategy that includes both full VM backups and separate backups of critical descriptor files, using tools like VMware Data Protection or third-party backup solutions. Best practices include maintaining proper file permissions, regularly validating backup integrity, documenting VM configurations, avoiding direct manipulation of VMDK files while VMs are running, using storage vMotion for migrations rather than manual file transfers, and keeping detailed records of VM disk configurations including disk geometry, adapter types, and hardware versions. Additionally, implementing a change management process for VM modifications and regularly monitoring VMDK file integrity can help identify potential issues before they lead to file corruption or loss.

Troubleshooting

When recreating VMDK descriptor files, common errors include incorrect disk size specifications, mismatched hardware versions, file permission issues, and invalid datastore path references. To resolve these issues, use vmkfstools to verify the flat file size (vmkfstools -v), ensure hardware version compatibility with your ESXi host, adjust permissions using chmod to match VMware requirements (typically 644), and double-check all datastore paths in the descriptor file.

Additional troubleshooting steps include validating disk geometry settings, confirming adapter type compatibility, and ensuring proper encoding of the descriptor file. For persistent issues, consulting VMware logs (/var/log/vmkernel.log) and comparing against known working descriptor files from similar VMs can help identify configuration discrepancies.

Conclusion

Recreating VMDK descriptor files requires careful attention to detail and proper configuration parameters. Regular backups remain the best defense against descriptor file loss.