OP_FREEZE errors with SyncDriver enabled while taking quiesced snapshots

[C P]

The majority of our Red Hat Linux (RHEL7 & RHEL8) servers have the SyncDriver enabled in /etc/vmware-tools/tools.conf and are able to perform VADP backups without issues.  On some servers, the quiesced snapshot creations will fail with OP_FREEZE errors for a specific filesystem.  You will see a similar error in /var/log/vmware-vmsvc-root.log:

[2024-10-31T06:05:57.335Z] [ warning] [vmsvc] [3310105] SyncDriver: '/opt/middleware' appears locked or frozen by another process.  Cannot complete the quiesced snapshot request.
[2024-10-31T06:05:57.335Z] [ warning] [vmbackup] [3310105] Error trying to perform OP_FREEZE on filesystems.

This issue is fixed by disabling the SyncDriver as below:

$ cat /etc/vmware-tools/tools.conf
[vmbackup]
enableSyncDriver=false

I can't seem to find much information about the SyncDriver online and the backups seem to be the same whether it's enabled or disabled.   Are there any ramifications to disabling the SyncDriver?   When this is disabled, does the vmtoolsd daemon freeze the filesystems using another method or is that step skipped?   I can hardly find any documentation online about the SyncDriver and as of a few years ago, this feature was deemed experimental and is disabled by default in the open-vm-tools package.   Is this still considered experimental or is this the recommended way to freeze a filesystem before creating a snapshot?

$ cat /etc/redhat-release 
Red Hat Enterprise Linux release 8.10 (Ootpa)

$ uname -r
4.18.0-553.22.1.el8_10.x86_64

$ rpm -qf /usr/bin/vmtoolsd
open-vm-tools-12.3.5-2.el8.x86_64

ESXi 7.0
vSphere Client version 7.0.3.01900

[vmotiontheinfo]

Hi 

I am not sure if you got this answered else where, however, let me try to put in whatever I am aware of about Sync Drivers.

Basically Sync Drivers, when enabled, flushes the data (present in the VM's Memory) to the disk and completes the quiescing process initiated by Backup softwares. Quiescing is nothing but temporarily pausing the IOPS on the VM so that the data can be backed up keeping it's consistency in mind. 

Now coming to your questions

>>> I can't seem to find much information about the SyncDriver online and the backups seem to be the same whether it's enabled or disabled.   Are there any ramifications to disabling the SyncDriver?   When this is disabled, does the vmtoolsd daemon freeze the filesystems using another method or is that step skipped?

Backups might still be failing and one of the reasons could be, not all applications support quiescing. Kindly make sure applications running on these VMs are compatible with the Sync Drivers. When Sync Driver is disabled, the result (most likely a data inconsistent snapshot) depends on the Guest OS and the Backup software which you're using.