A VMware ESXi host uses an dual-image architecture in which the boot disk includes two partitions on which the ESXi image is stored. The partitions are referred to as boot banks. One boot bank contains the active image and the second the previous image. When an update is deployed, the active image is copied from the primary book bank to the alternate book bank and the new image is installed into the primary book bank. To fall back to the alternate image, reboot the host and press “Shift+R” when the screen displays “Loading VMware Hypervisor.”
Press “Y” and then Enter to reboot to the previous image.