Reducing or disabling excessive vSAN CnsSync warnings

Products

• VMware vCenter Server

Issue/Introduction

Customers may experience excessive Info-level logging from VMware vSAN, specifically warnings related to datastore synchronization (CnsSync). The errors indicate that datastores cannot be synchronized due to missing or incomplete records, resulting in thousands of similar log entries per hour. The CnsSync messages can also be seen in a non-vSAN enabled environment as well. 

Example log message:

YYYY-MM-DDT00:00:00.warning vsanvcmgmtd[264989] [vSAN@6876 sub=CnsSync] Cannot sync datastore ds:///vmfs/volumes/UUID/, without all records

Environment

vCenter 7.x

vCenter 8.x

Cause

The frequent occurrence of CnsSync warnings is caused by the vSAN component's default setting for the CNS (Content Storage Node) synchronization interval. By default, this interval is set to 1 minute, leading to a high volume of Info-level logs that are generated every time the synchronization process attempts to sync datastores.

Resolution

To reduce the frequency or disable these CnsSync warnings, modify the synchronization interval based on your specific vCenter version.

For vCenter 8.0.3 Patch 05 and later:

1. Identify the path to the VsanVcMgmtConfig.xml file on your vSAN management node.

2. This file is typically located in /usr/lib/vmware-vsan/VsanVcMgmtConfig.xml.

3. Open the VsanVcMgmtConfig.xml file using a text editor.

4. Locate the <property name="newSyncInterval">60</property> entry.

5. Change the value of 60 to 0. This disables periodic sync.

6. Save the changes to the VsanVcMgmtConfig.xml file.

7. To apply configuration changes, the service must be restarted using the following command via SSH:

     service-control --restart vmware-vsan-health

 

For vSphere 7.x and versions prior to vCenter 8.0 U3 Patch 05:

1. Identify the path to the VsanVcMgmtConfig.xml file on your vSAN management node.

2. This file is typically located in /etc/vmware/vsan/config/. In versions prior to vCenter 8.0 U3 the file is located at /usr/lib/vmware-vpx/vmware-vsan.

3. Open the VsanVcMgmtConfig.xml file using a text editor.

4. Locate the <property name="newSyncInterval">60</property> entry.

5. Change the value of 60 to a very large number (e.g., 2,147,483,647 seconds). This effectively disables frequent synchronization intervals and reduces log volume.

6. Save the changes to the VsanVcMgmtConfig.xml file.

7. Restart the vSAN management services for the changes to take effect. 

      service-control --restart vmware-vsan-health

Additional Information

• The CnsSync log entries are expected once after a restart of the system or when there is a change in the environment that triggers synchronization.

• Setting the synchronization interval to an extremely large value does not impact vSAN functionality, as it only affects the frequency of the logging process.

• This adjustment reduces unnecessary log volume without affecting data consistency.