With the introduction of vSphere 5.0, ESX has been discontinued. ESXi is now the only version available for datacenter server virtualization. Due to the architectural changes from ESX to ESXi, not all configuration files, settings, and third party tools are guaranteed to be migrated to ESXi 5.x. Ensure that you retain and note any configuration modifications before performing an upgrade. For more information, see the vSphere Upgrade Guide.Note: VMware strongly recommends that you make a backup of your virtual machines if they are located on local storage of the ESX/ESXi host before upgrading.
Note: To determine whether your server has 64-bit VMware support, download the CPU Identification Utility from vmware.com.
Note: ESXi does not support using local, internal SATA drives on the host server to create VMFS datastores that are shared across multiple ESXi hosts.
ESXi 5.1 has these storage requirements: