ESXi hosts can be upgraded from previous version or from ESXi 4.x in several ways. ESXi Installable 4.x hosts can be upgraded in one of three ways:
If we have implemented Auto Deploy, we can directly apply a new image and reboot.
While upgrading VMware ESXi hosts from a previous version of ESXi 4.x to the latest version of 5.x using any of the three supported approaches, 50 MB must be accessible on the local VMFS volume. This space is required to store the ESXi server's configuration data in temp mode.
The following table illustrates approaches for upgrading ...