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vSAN Health Service - Cluster Health – CLOMD liveness check (2109873)

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This article explains the Cluster Health – CLOMD liveness check in the vSAN Health Service, and provides details on why it might report an error.

CLOMD (Cluster Level Object Manager Daemon) plays a key role in the operation of a vSAN cluster. It runs on every ESXi host and is responsible for new object creation, initiating repair of existing objects after failures, all types of data moves and evacuations (For example: Enter Maintenance Mode, Evacuate data on disk removal from vSAN), maintaining balance and thus triggering rebalancing, implementing policy changes, etc.

It does not actually participate in the data path, but it triggers data path operations and as such is a critical component during a number of management workflows and failure handling scenarios.

Virtual machine power on, or Storage vMotion to vSAN are two operations where CLOMD is required (and which are not that obvious), as those operations require the creation of a swap object, and object creation requires CLOMD.

Similarly, starting with vSAN 6.0, memory snapshots are maintained as objects, so taking a snapshot with memory state will also require the CLOMD.


Q: What does the “Cluster health – CLOMD liveness check” check do?

This checks if the Cluster Level Object Manager (CLOMD) daemon is alive or not. It does so by first checking that the service is running on all ESXi hosts, and then contacting the service to retrieve run-time statistics to verify that CLOMD can respond to inquiries.

Note: This does not ensure that all of the functionalities discussed above (For example: Object creation, rebalancing) actually work, but it gives a first level assessment as to the health of CLOMD.

Q: What does it mean when it is in an error state?

CLOMD may still have issues, but this test does a very basic check to make sure that it can process requests. If this reports an error, the state of the CLOMD process needs to be checked on the relevant ESXi host.

A good way to further probe into CLOMD health is to perform a virtual machine creation test (Proactive tests), as this involves object creation that will exercise and test CLOMD thoroughly.

For more information about this issue, refer to the following article: vSAN CLOMD daemon may fail when trying to repair objects with 0 byte components (2149968).

Q: How does one troubleshoot and fix the error state?

If any of the ESXi hosts are disconnected, the CLOMD liveness state of the disconnected host is shown as unknown. If the Health service is not installed on a particular ESXi host, the CLOMD liveness state of all the ESXi hosts is also reported as unknown.

If the CLOMD service is not running on a particular ESXi hosts, the CLOMD liveness state of one host is abnormal.

For this test to succeed, the health service needs to be installed on the ESXi host and the CLOMD service needs to be running. To get the state status of the CLOMD service, on the ESXi host, run this command:

/etc/init.d/clomd status

If the CLOMD health check is still failing after these steps or if the CLOMD health check continues to fail on a regular basis, open a support request with VMware Support. For more information, see How to file a Support Request in My VMware (2006985).

Additional Information

See Also

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