The vCenter Host Agent Pre-Upgrade Checker produces a report showing known issues that might prevent a successful upgrade of the vCenter Host Agent software.
To ensure a successful upgrade to vCenter Server 5.x, you must diagnose and fix any potential problems on the managed ESX/ESXi hosts. You can run the vCenter Host Agent Pre-Upgrade Checker for in-place upgrades from vCenter Server 4.x to vCenter Server 5.x.
vCenter Host Agent runs on all managed ESX/ESXi hosts. This software coordinates actions received from vCenter Server. When you add a host to vCenter Server, the agent is installed on the physical ESX/ESXi host. When you upgrade to vCenter Server 5.x, the agent residing on each ESX/ESXi host must be upgraded as well.
During a vCenter Server upgrade, the existing agent software is uninstalled and the updated agent software is installed in its place. If the upgrade fails, the updated agent software might not be installed and the host might become unreachable by vCenter Server 4.x or 5.x. To avoid this condition, you can run the vCenter Host Agent Pre-Upgrade Checker before you try to upgrade to vCenter Server 5.x.
The vCenter Host Agent Pre-Upgrade Checker checks to make sure that the agent software is ready to be upgraded. Some of the checks include checking to make sure that the host is reachable, the disk space is sufficient, the network is functioning, the file system is intact, and required patches are applied. Each time you run the tool, the system queries VMware.com and downloads any new updates for the tool. This action ensures that as new upgrade issues are discovered, the tool remains as useful as possible.
A successful vCenter Host Agent pre-upgrade check does not guarantee a successful upgrade to vCenter Server 5.x. An upgrade to vCenter Server involves multiple components, and the tool checks only one component: the vCenter Host Agent. Also, the tool checks only known issues. Other issues might be present that the tool does not check.
The vCenter Host Agent Pre-Upgrade Checker does not fix the reported issues. You must resolve the reported issues manually and rerun the tool to verify that the issues are resolved.
For the procedure to run the vCenter Host Agent Pre-Upgrade Checker, see Run the vCenter Host Agent Pre-Upgrade Checker.