We currently have a vSphere environment consisting of 3 hosts running ESX 4.1 and vCenter server 4.1. These 3 hosts are connected via fiber to an EMC Clariion CX4 where all the VMs reside.
We are replacing the existing host hardware with 3 new rack servers and I'm in the process of nutting out a plan of attack for upgrading these hosts. I was also thinking this would be a good opportunity to move from ESX to ESXi.
I have enough capacity to run all VMs comfortably on just 2 hosts for a short period of time.
Can I simply vMotion all vm's off one host, install ESXi on the replacement, configure it up in vCenter and get visibility to the CX4 and then vMotion hosts back onto it, then repeat for host 2 & 3?
yes this is possible. provided that the family of the CPU for the old and new hosts are in the new family and same manufacturer (intel-intel or amd-amd). if not then you will need to turn on enhanced vmotion compatibility in which may required downtime for the virtual machines.