Hi i am studying for an interview where i want to know the process required for upgrade process for VMWare ESXi 4.0 to 5.1 to 5.5? What do we upgrade first VCenter or ESXi or VMS? What process do we have to follow and which tools do we use?
Before beginning any upgrade, make sure that the hardware is compatible with the version of VMware you want to install. This can be verified using the VMware HCL. Also, make sure that the ESX version is compatible with the VM guest OS. On occasions there are legacy systems on extremely outdated versions of Windows that get virtualized. Plan for downtime. Upgrading VM hardware and VMware tools require reboots. If this is not planned it can result in unplanned outages, downtime, etc.
You upgrade vCenter first, followed by the host and lastly VMware tools and virtual machine hardware version on VMs. Be careful when upgrading the virtual machine hardware. Upgrading to the latest VM hardware removes some of the manageability from the vSphere desktop client and forces you to use the web client.
You can also use update manager to schedule host upgrades, patching, etc as well as VMware tools deployment. This is just an overview; there is obviously more to it than this.