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 5.0. VMware has put together an article detailing the best practices for upgrading. Some of the steps noted in the article include:
- Your hardware is compliant on the VMware Compatibility Guide.
- You have a 64-bit processor. VMware ESXi 5.0 only installs and runs on servers with 64-bit x86 CPUs. It also only supports LAHF and SAHF CPU instructions.
- Intel VT is enabled in the host's BIOS.
- You have 2GB RAM. This is the minimum required to install.
- You have one or more Gigabit or 10GB Ethernet controllers. For a list of supported network adapter models, see the VMware Compatibility Guide.
- You have a SCSI disk or a local, non-network, RAID LUN with unpartitioned space for the virtual machines. For Serial ATA (SATA), disk connected through supported SAS controllers or supported on-board SATA controllers. SATA disks are considered remote, not local. These disks are not used as a scratch partition by default because they are seen as remote.
Also, be sure to check out the white paper titled "What's New in VMware vSphere 5.0 Platform"