What CPU characteristic can cause a vSphere vMotion migration to fail if there is a mismatch?

vSphere vMotion migrations rely on the underlying CPU compatibility between the source and destination hosts to ensure that virtual machines operate seamlessly during the migration process. When considering the characteristics of CPUs, hyperthreading is a critical factor that can lead to migration failures if there is a mismatch.

Hyperthreading allows a single CPU core to act as two logical processors, which can significantly enhance performance by enabling better utilization of CPU resources. If one host supports hyperthreading while the other does not, it creates an inconsistency in the way CPU resources are exposed to virtual machines. This difference can cause vMotion to fail because the guests may run differently based on the available logical processors, leading to potential performance issues or instability if they were to switch hosts.

Understanding this essential feature is crucial because it directly affects how virtual machines utilize the physical resources. In contrast, other characteristics like core count, CPU architecture, and cache size, while important, do not have as direct of an impact on the immediate compatibility required for vMotion, especially if the CPU features set of the hosts align regarding instruction sets and capabilities. Thus, hyperthreading stands out as a defining characteristic that can lead to migration failures when mismatched.