Recreating a missing virtual machine disk (VMDK) descriptor file

Posted: April 30, 2013 in VMware
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Each disk drive for a virtual machine consists of a pair of .vmdk files. One is a text file containing descriptive data about the virtual hard disk, and the second is the actual content of that disk. For example, a virtual machine named examplevm has one disk attached to it. This disk is comprised of a examplevm.vmdk descriptor file of under 1 KB, and a 10 GB examplevm-flat.vmdk flat file which contains virtual machine content.

This article helps you to recreate a lost virtual disk descriptor file.

Detailed steps

To create a virtual machine disk:

  1. Log into the terminal of the ESXi/ESX host:
  2. Navigate to the directory that contains the virtual machine disk with the missing descriptor file using the command:# cd /vmfs/volumes/myvmfsvolume/mydir

    Note:

    • If you are using a version of ESXi, you can access and modify files and directories using the vSphere Client Datastore Browser or the vifs utility included with the vSphere CLI. For more information, see the section Performing File System Operations in the vSphere Command-Line Interface Documentation.
    • If you are using VMware Fusion, the default location for the virtual machine files is the home/Documents/Virtual Machines.localized/virtual_machine/ folder, where home is your home folder, and virtual_machine is the name of the virtual machine.
  3. Identify the type of SCSI controller the virtual disk is using. You can do this by examining the virtual machine configuration file (.vmx). The controller is identified by the line scsi#.virtualDev, where # is the controller number. There may be more than one controller and controller type attached to the virtual machine, such as lsisas1068 (which is the LSILogic SAS controller), lsilogic, or buslogic. This example uses lsilogic:scsi0.present = “true”
    scsi0.sharedBus = “none”
    scsi1.present = “true”
    scsi1.sharedBus = “virtual”
    scsi1.virtualDev = “lsilogic”
  4. Identify and record the exact size of the -flat file using a command similar to:# ls -l vmdisk0-flat.vmdk

    -rw——- 1 root root 4294967296 Oct 11 12:30 vmdisk0-flat.vmdk

  5. Use the vmkfstools command to create a new virtual disk:# vmkfstools -c 4294967296 -a lsilogic -d thin temp.vmdk

    The command uses these flags:

    • -c sizeThis is the size of the virtual disk.
    • -a virtual_controllerWhether the virtual disk was configured to work with BusLogic, LSILogic (for both lsilogic and lsilogic SAS) or IDE.
    • -d thinThis creates the disk in thin-provisioned format.

    Note: To save disk space, we create the disk in thin-provisioned format using the type thin. The resulting flat file then consumes minimal amounts of space (1 MB) instead of immediately assuming the capacity specified with the -c switch. The only consequence, however, is the descriptor file contains an extra line that must be manually removed in a later step.

    The temp.vmdk and temp-flat.vmdk files are created as a result.

  6. Delete temp-flat.vmdk, as it is not needed. Run the command:# rm temp-flat.vmdk
  7. Rename temp.vmdk to the name that is required to match the orphaned .flat file (or vmdisk0.vmdk, in this example):# mv temp.vmdk vmdisk0.vmdk
  8. Edit the descriptor file with a text editor:
    1. Under the Extent Description section, change the name of the .flat file to match the orphaned .flat file you have.
    2. Find and remove the line ddb.thinProvisioned = “1” if the original .vmdk was not a thin disk. If it was, retain this line.# Disk DescriptorFile
      version=1
      CID=fb183c20
      parentCID=ffffffff
      createType=”vmfs”

      # Extent description
      RW 8388608 VMFS “vmdisk0-flat.vmdk”

      # The Disk Data Base
      #DDB

      ddb.virtualHWVersion = “4”
      ddb.geometry.cylinders = “522”
      ddb.geometry.heads = “255”
      ddb.geometry.sectors = “63”
      ddb.adapterType = “lsilogic”
      ddb.thinProvisioned = “1”

      The virtual machine is now ready to power on. Verify your changes before starting the virtual machine.

      If powering on the virtual machine is not successful, see Troubleshooting a virtual machine that is unable to power on (2001005).

  9. To check the disk chain for consistency, run this command against the disk descriptor file:For ESXi 5.0:
    # vmkfstools -e filename.vmdk

    For a complete chain, you see output similar to:
    Disk chain is consistent

    For a broken chain, you will see a summary of the snapshot chain and then an output similar to:
    Disk chain is not consistent : The parent virtual disk has been modified since the child was created. The content ID of the parent virtual disk does not match the corresponding parent content ID in the child (18)

    For ESXi 3.5/4.x:
    # vmkfstools -q filename.vmdk

    For a complete chain, you see output similar to:
    filename.vmdk is not an rdm

    For a broken chain, you see output similar to:
    Failed to open ‘test-000001.vmdk’ : The parent virtual disk has been modified since the child was created (18)

Ref : http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1002511

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