Just keep in mind that certain changes from older versions should be identified before upgrading to enable a smooth transition. These are just some pointers for what should be thought about from the outset.
As with most new versions of software, there are always simple things that might cause unnecessary pain. The main thing to point out is that if you upgrade your ESX or ESXi hosts to vSphere 4.1 first then you won’t be able to add them to vCenter 4.0.x or older so the best process would be to upgrade vCenter first to 4.1 as this is compatible and supports the current latest version of ESX and ESXi hosts along with the older versions.
An annoying yet simple problem that you may encounter if you use VMware Update Manager (VUM) was posted over on Duncan Epping’s great site Yellow Bricks where he pointed out that although vSphere 4.1 requires 64-bit, VUM required a 32-bit ODBC DSN. This may be confusing as VUM does actually require a 64-bit OS but it’s good to know and it is stated in the VUM Install Guide.
So continuing on about the 64-bit requirement, depending on what version of OS you used when installing your older versions of vCenter will depend on your upgrade/migration process. For those of you that installed a 32-bit OS, which I can imagine a lot of us did, you will need to provision a new 64-bit OS for the job. This might be a good time, if you installed your vCenter on hardware based servers, to think about if you want to move to a virtual machine (VM) instead. This is obviously down to your preference and environment but it’s worth having a look though the latest best practices and release notes to make up your own mind. Either way, don’t forget your backups. As with any upgrade/migration it’s always good practice to get a working backup first.
Moving on, we have the retirement of ESX in the pipeline. As announced by VMware, vSphere 4.1 is the last significant release that will support ESX. What does this mean, well in a nutshell, so to speak, it’s time to start the move over to ESXi. I’m not saying to ditch all your ESX servers and start again but you need to start planning for a phased out approach of the ESX servers and all new servers to be ESXi. VMware now say ‘Upgrade from ESX to ESXi to improve security and simplify hypervisor management’. What a nice way of saying bye bye ESX. More info on this can be found here.
--> The rest is on the XtraVirt site :