I'm looking at doing the same upgrade/migration of ESX 4.1 to 5.1 and based on the comments here I have some questions:
1. If I currently have a physical server running vCenter 4.1 and I want to migrate it to a new machine using KB 5850444 minus the need to move the databases since those are on a separate physical SQL cluster server and will stay in the same location and I then build a new VM running vCenter 5.1 does that mean that I can use the same name and IP address for the new vCenter 5.1 server? Step 2 of the article states to shutdown the vCenter service of the original server that's why I'm asking.
2. I have new server hardware for my ESXi 5.1 hosts and SAN shared storage that will have new VMFS-5 datastores to keep this new environment separate to my existing one that's using ESX 4.1 and VMFS-3 datastores. So, if I build a new VM for vCenter as stated above and use existing database my understanding is that my ESX 4.1 hosts will show up in my new vCenter 5.1...correct? I can then upgrade using Update Manager the hosts to ESXi 5.1 then the VMs, etc. is that correct? **Correction...I don't want to upgrade my ESX 4.1 hosts...new hardware will take their place...I just want them in my vCenter 5.1 so that I can easily move VMs onto the new hosts, etc.
3. Or will it be better for me to start with a fresh new install including the databases for vCenter 5.1 and remove ESX 4.1 from original vCenter 4.1 to then add to 5.1? I'm not worried about history data, so starting from scratch is an option for me if it still allows for a smooth upgrade/migration with zero downtime for the host part. I know that for the VM hardware upgrade I will need to schedule downtime, but for everything else I'm looking at zero downtime to accomplish it.
4. Assuming that the answer to my questions above allows me to have a new vCenter 5.1, managing my ESX 4.1 hosts, my VMs that are on a VMFS-3 datastores, and hardware version 7...If I upgrade them using Update Manager can they be moved to the new VMFS-5 datastores? or would I have to do a cold migration to move them from VMFS-3 to VMFS-5 datastores?