Hmm, I suspected it was wishful thinking on my part. So both of the above responders suggested pretty much the same thing. That indeed was my initial plan of attack. Although I was thinking of it as a legitimate upgrade path, not a workaround; that worries me a bit that you called it that Frank. Anyhow, my current hosts are all ESX 4.1 by the way; nonetheless I know vCenter 5.1 can manage both ESX and ESXi 4.0 and up, so I'm good there. However the folks who I recently inherited my environment from, strongly and repeatedly advised to do a brand new install of everything because they ran into lots of problems with inplace upgrades in the past. Having read your replies though, I am brainstorming about this method again since if I do a new install of the vCenter Server 5.1 and do a new install of each ESXi 5.1 I will in effect honor the advice of doing a new install and at the same time keep the environment intact and will be able to do vMotion potentially with no or little downtime instead of using Converter to bring VMs over to a totally new vSphere environment, with definite downtime. The main goal however is to preserve a reliable roll-back process. If my above thinking is copacetic maybe you can review help me with the sequence of events to take place:
1 evict first ESX 4.1 host from the cluster and disconect it from vCenter (without any VMs on it)
2 do a new instal of ESXi 5.1U1 on the first host
3 loggon to the new ESXi host with vSphere client
4 storage and settings (* This is tricky - WWNs do not change so I assume ESXi 5.1 will see all the LUNs that were presented to it when it was ESX 4.1, right? But it will see it as a non-configured storage devices, wont it? And Adding it would format it as VMSF5 destroying any VMs on it? If that's true then I will need to free up or get some extra LUNs from my SAN people, yes? )
5 provision a VM for vCenter
6 install and configure vCenter server and components on the VM
7 login to the new vCenter 5.1 with Web Client (can I still do all the bellow steps in vSphere client? I played with Web Client in a nested environment - so slow)
8 configure Networking (mimicking the old environment): Uplinks, vSwitch, Distributed Switch/Port Groups (**Do i need to do the vDS or will it move over with 4.1 hosts?)
9 configure HA/DRS Cluster and related settings and Add the first ESXi 5.1 host to Cluster (* I am able to have only one host in a cluster, right?)
10 configure a temporary Cluster for 4.1 hosts
11 configure/mimic Resource Pools and folder structure
12 Disconnect the rest of the 4.1 hosts from vCenter 4.1;
13 connect 4.1 hosts to new vCenter 5.1 and add them to the temp Cluster (** now during this step - what happens to the Distributed Switch? does it move over? does it break? do 4.1 hosts see the port groups of vDS I presumable mimicked in the above step?)
14 vMotion a small number of test/dev VMs to the 5.1 host; svMotion to VMFS5 LUNs
15 Upgrade VMware Tools and virtual Hardware version after the a few weeks of smooth operation.
16 Repeat above steps for the rest of the 4.1 hosts and VMs.
17 Remove the temporary Cluster
Please comment on anything I missed or misinterpreted.
Many thanks.
