• Bad entries in virtual disk descriptor files (*.vmdk, *.vmx)
• Communication problems between ESXi host and storage array
• ESXi OS problems
• Problems with file locks
• Virtual disk data corruption

• VM sharing disks
• VM file locks
• Incorrect disk file sizes
• Missing virtual disk files
• Bad virtual disk descriptor files
• vSAN cluster problems
• Snapshot virtual disk problems
• Interrupted snapshot consolidation
• VM descriptor file problems
• Lost VM process
• Storage errors

Check for VM sharing disks with other VMs

1. Determine which virtual disk files are being used by the VM:
   1. Connect to the command line for the host managing the VM per Connecting to an ESX host using an SSH client
   2. Get the names of the virtual disk files currently attached to the VM per Get virtual machine file path and virtual disk information through ESXi command line
2. Follow Determining if a virtual disk is attached to another virtual machine
3. If the VM has disks attached to other VMs:
   1. Ensure the configuration of the VM and shared virtual disk is correct per Enabling or disabling simultaneous write protection provided by VMFS using the multi-writer flag
   2. For Microsoft Cluster VMs please ensure VM and virtual disk configuration is set up correctly per About Setup for Windows Server Failover Clustering on VMware vSphere
   3. In some cases you may need to vMotion the affected VM to the host where the other VM resides to overcome file lock problems

Check for VM file locks

• Follow Investigating virtual machine file locks on ESXi hosts

Check for incorrect VM virtual disk data file sizes

1. Connect to the command line for the host managing the VM per Connecting to an ESX host using an SSH client
2. Get the names of the virtual disk files currently attached to the VM per Get virtual machine file path and virtual disk information through ESXi command line
3. Compare the sizes of the virtual disk data files (*-flat.vmdk) to the last known correct sizes of the file
   1. Example: You know from experience, or from looking at backup files, that a virtual disk should be 700 GB but it is showing as 400 KB.
   2. If the file is suspect, either
      1. Rebuild the virtual disk
      2. Restore the virtual disk from backup

Check for missing VM virtual disk files (*.vmdk)

• Follow the "Check if virtual disk files are missing:" section in the KB article  Error: Can't open 'vmfs/volumes/.vmdk': Could not find the file" while powering on virtual machine

Check for bad data in VM virtual disk characteristics file (*.vmdk)

1. Determine which virtual disk files are being used by the VM:
   1. Connect to the command line for the host managing the VM per Connecting to an ESX host using an SSH client
   2. Get the names of the virtual disk files currently attached to the VM per Get virtual machine file path and virtual disk information through ESXi command line
   3. For any virtual characteristics file (*.vmdk), run the command, replace the type in italics with the vmdk file name:

Check for vSAN cluster problems

Check for snapshot virtual disk problems

Check for cancelled or interrupted snapshot virtual disk consolidation

Check for bad data in VM descriptor file (*.vmx)

1. Connect to the command line for the host managing the VM per Connecting to an ESX host using an SSH client
2. Get the names of the virtual disk files currently attached to the VM per Get virtual machine file path and virtual disk information through ESXi command line
3. If any of the virtual disk files listed look incorrect:
   1. Make a backup of the VM descriptor file, using the following command, where the text in italic is replaced by the name of the VM:

2. Re-create the descriptor file by following Recreate a lost or deleted virtual machine .vmx configuration file on an ESXi host

Check for lost VM process control

Check for storage array errors

1. Check the vCenter or ESXi user interface for errors related to the datastore the VM is on
2. Connect to the command line for the host managing the VM per Connecting to an ESX host using an SSH client
3. Get the names of the virtual disk files currently attached to the VM per Get virtual machine file path and virtual disk information through ESXi command line
4. If there are any input/output errors, or I/O errors, reported on the command line, please check the storage array for problems. You may need to contact your array vendor for further diagnosis and troubleshooting.
5. Check the ESXi logs for further critical storage array errors per Storage vMotion fails with error "Failed to copy one or more disks"

• "File system specific implementation of LookupAndOpen [file] failed" in vmware.log file
• Race condition on ESXi 6.0 and 6.5 causing disruption to VMs or hostd management service
• VM fails to power on with Error: "File system specific implementation of LookupAndOpen [file] failed"
• Failed to power on virtual machine

• Reconfiguring a VM to different virtual disks can cause data loss.
• Restarting management agents can cause vMotion to to be unavailable.