VMware

How to use VOMA

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The VMware On-disk Metadata Analyzer (VOMA) tool is a utility designed to check VMFS volumes for metadata inconsistencies and corruption. It can check VMFS3 and VMFS5 file systems and is particularly useful for troubleshooting datastores.

VOMA tool can be used in various scenarios to validate and check VMFS volumes for metadata consistency on LUNs. Below are several scenarios where VOMA could be useful, along with explanations and steps for validating LUNs:

Scenario 1: After Storage Migration or LUN Movement

  • Use Case: When a LUN has been migrated between storage arrays or within the same array.
  • VOMA Execution: Run VOMA to check for any metadata inconsistencies post-migration.
  • Validation: If VOMA reports no issues, you can consider the LUN to be healthy post-migration.

Scenario 2: Suspected Corruption or Inconsistency

  • Use Case: If there is a suspicion of corruption or inconsistency on a VMFS datastore.
  • VOMA Execution: Run VOMA to confirm the presence of any corruption or inconsistencies in the VMFS metadata.
  • Validation: If VOMA does not report any issues, the suspected corruption likely does not exist in the metadata of the VMFS volume.

Scenario 3: After a SAN Crash or Network Glitch

  • Use Case: Post a SAN failure or a network glitch causing disruptions in storage access.
  • VOMA Execution: Run VOMA to check the integrity of the VMFS metadata after restoring access.
  • Validation: If no errors are reported by VOMA, the VMFS volume is likely in a consistent state post-recovery.

However, it is important to note that VOMA can only identify problems but cannot fix them.

Basic Syntax:

The basic syntax of VOMA is as follows:

voma -m vmfs -f check -d <device>

Where <device> is the path to the device you want to check, typically something like /vmfs/devices/disks/naa.xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.

Using VOMA Tool:

  1. Access ESXi Shell or Secure Shell (SSH):
    • You can access the ESXi shell directly from the console or remotely by enabling and connecting via SSH.
  2. Identify the Device:
    • Run the following command to list all VMFS datastores and their device paths:
esxcli storage vmfs extent list
  1. Run VOMA on the Desired Device:
    • Once you have identified the device path, use the VOMA tool to check the VMFS volume.

Example:

Assuming that the device path you want to check is /vmfs/devices/disks/naa.1234567890abcdef1234567890abcdef, you would run the following command:

voma -m vmfs -f check -d /vmfs/devices/disks/naa.1234567890abcdef1234567890abcdef

Considerations:

  • Read-Only Analysis: VOMA performs read-only analysis, meaning it doesn’t make any changes to the VMFS volumes it checks.
  • Active Volumes: It’s generally safe to run VOMA on active VMFS volumes, but because it is a resource-intensive process, it’s best to run it during a maintenance window or low-activity period.
  • Documentation: Any issues detected by VOMA should be documented along with the output of the command.
  • VMware Support: If VOMA identifies errors, it’s usually advisable to contact VMware Support for further assistance, as the tool does not provide repair functionalities

When running VOMA to check VMFS metadata, if there are inconsistencies or corruptions, it will provide output detailing the detected errors. Below are a few hypothetical examples of what you might encounter and what it could imply:

Example 1: Metadata Block Corruption

Error: Metadata block (XXXXXX) is corrupted on volume "Volume_Name".
  • Implication: This could imply that there is some corruption within the metadata block mentioned. Metadata blocks store essential information about the filesystem, so corruption here is a critical issue.

Example 2: Reference Count Mismatches

Error: Reference count mismatch detected: (XXXXX != YYYY) for Block XXXX on volume "Volume_Name".
  • Implication: Reference count mismatches usually mean that there is a discrepancy in the number of links pointing to a block. This could potentially lead to data integrity issues.

Example 3: Missing Heap Entries

Error: Missing heap entry detected on volume "Volume_Name".
  • Implication: Missing heap entries can imply that there is metadata corruption affecting the allocation of space within the VMFS volume.

Example 4: On-disk Locking Errors

Error: On-disk locking error detected on volume "Volume_Name".

Action Steps:

  1. Document Errors: Carefully document all errors reported by VOMA.
  2. Engage VMware Support: Since VOMA is a diagnostic tool and does not repair the detected errors, you would typically need to engage VMware Support for further analysis and remediation steps.
  3. Data Integrity Check: Review the data stored on the LUN for any signs of corruption or loss, especially if critical data is stored on the affected LUN.
  4. Backups and Snapshots: Ensure that all affected VMs and data are backed up, and consider taking snapshots of the VMs before attempting any remediation.
  5. Review SAN Logs: Check the logs of your SAN for any errors or signs of issues that might have caused the corruption, such as disk failures or network errors.
  6. Performance Monitoring: Monitor the performance of the affected LUN and VMs for any abnormalities or degradation that might be related to the corruption.

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