What action should an administrator take to increase the number of simultaneously migrating virtual machines from four to eight?

To increase the number of simultaneously migrating virtual machines from four to eight, adding a 10GigE (10 Gigabit Ethernet) network card to each ESXi host is the most effective action. This option enhances the network bandwidth available for data transfer during migrations, allowing more traffic to flow concurrently. Since vMotion, the technology used for migrating virtual machines, relies heavily on network performance, a faster network connection directly impacts the ability to perform multiple migrations at once without degradation in performance.

This increase in bandwidth facilitates larger volumes of data to be moved simultaneously, which is particularly beneficial when scaling up operations. When dealing with multiple virtual machines, having a higher throughput capability helps ensure that the migration process remains efficient and swift, minimizing the impact on services.

In contrast, while adding more memory to the ESXi hosts might improve performance and resource availability for running virtual machines, it does not specifically address the limitations of the network bandwidth during migration. Port mirroring is a network management technique primarily used for monitoring traffic, and it typically does not contribute to improving migration capabilities. Lastly, configuring load balancing would be essential in distributing workloads evenly among hosts, but it does not inherently increase the capacity for simultaneous migrations like upgrading the network infrastructure does.