What must VMs not have before enabling SMP-FT?

Before enabling SMP Fault Tolerance (SMP-FT) on virtual machines (VMs), it is essential that they do not have any snapshots. This requirement is crucial because snapshots can interfere with the state consistency that SMP-FT necessitates for its operation. When SMP-FT is enabled, the VM's primary instance and its secondary instance need to remain synchronized to ensure continuous availability and data integrity. If there are snapshots present, they introduce additional complexity, as they represent a point-in-time state of the VM that may cause discrepancies between the primary and secondary instances. Therefore, to maintain the consistent and reliable operation that SMP-FT seeks to provide, any existing snapshots must be removed prior to enabling this feature.

The other options do not pose similar issues with SMP-FT compatibility. For instance, CD-ROM drives, templates, and thin provisioned disks do not affect the synchronizing process required for SMP-FT; thus, their presence or absence does not impact the ability to enable this high-availability feature.