ESXi hosts deployed using Auto Deploy requires the Auto Deploy server to be available and reachable every time the host reboots. Prior to vSphere 5.1, if the network boot failed, the server did not have a source to continue the boot process. Starting with vSphere 5.1, you can enable stateless caching that will add a level resiliency in case the network boot (PXE boot) fails. The stateless caching mode can be enabled by editing the host profile associated to the ESX host.
The ESXi host should have local storage for stateless caching to work.
The following procedure will guide you through the steps required to enable stateless caching: