I am in process of moving VMs from Vcenter 5.1 to vCenter 5.5.
Esxi hosts in VC 5.1 and VC5.5 have access to same datastore.
In order to move
VMware ESX needs to know if this virtual machine was moved or copied. If you don't know, answer "button.uuid.copiedTheVM".
I choose option that I moved it. Why should I get this message? What happens if choose I moved it ?and what happens if I choose I copied it ?
The mechanism is explained in this article:
In you case you should go with "I moved it" it. Otherwise, when you select the copy option, it will generate a new UUID and a new MAC address for the vNIC as well, which in most cases causes the GuestOS to lose static IP information.
By the way, you don't need to incorporate downtime for your VMs for this migration if you already have shared storage and network access. You can just disconnect hosts from the old vCenter and add them to the new one, and then vMotion the VMs to the new hosts.