We are budgeting for more licensing and hardware for 2014 and want to do this right away in January. I am trying to decide what is the best order of operations for adding two additional vmware hosts to our current vsphere installation, and also upgrading our vsphere / esx 4.1 u3 to the latest and greatest.
We have 3 Dell PowerEdge R710's running ESX 4.1 U3. In this vmware cluster there is a vcenter server 4.1 U3 virtual machine managing this. All three servers are about 90% memory utilized so we are adding 2 additional servers. Likely the Dell PowerEdge R620 since we can fit 2 in the space of a 710. The storage is on an EMC NX4 NFS san which will be upgraded also but not yet, let's just tackle the vmware part of it.
When adding 2 additional R620's, should I install ESX 4.1 on them and join them to the existing cluster, and THEN upgrade vcenter, and each esx one by one? Reason I ask is because at 90% usage on the 3 current servers, I need the 2 additional servers to support operations while upgrades are taking place. They would be able to hold vm's vmotioned off while each host is getting upgraded one at a time.
So is that the best way to go about adding hosts and upgrading? Would I add them as 4.1's, then they would be available as vmotion targets so I have room to start upgrading hosts one at a time?
If I update vcenter to the latest version, it is backwards comparable and can manage the 4.1 hosts as well as 5.x hosts? I suppose version 5.5 is the latest that I would be receiving from VMWare? It's ESXi right, so how is that upgrade from ESX 4.1 to ESXi 5.5? How much storage space do I need for ESXi 5.5, as I am specking out these Dell R620's and need to know how much hard drive to put in.