Inside the Sphere
I've had vSphere 4 (otherwise known as ESX 4.0 and vCenter 4.0) running in the lab for a few days now. It comprises the same parts as VI3, with ESX or ESXi running on the hosts, and vCenter running the show. Installation of these components is the same as it's always been, only now you're prevented from installing vCenter on an Active Directory domain controller, which is arguably a good idea. In fact, VMware now recommends running vCenter as a VM.
My early testbed comprised several different boxes, with a mix of Intel- and AMD-based servers, including an HP ProLiant DL580 G5 and a Sun Fire X4600 M2. I installed vCenter as a VM running under Windows Server 2008, alongside a separate domain controller, and built myself a nice little virtual infrastructure.
As I mentioned, the new Fault Tolerance feature has the ability to change lives. In a nutshell, this allows you to run the same VM in tandem across two hardware nodes, but with only one instance actually visible to the network. You can think of it as OS-agnostic clustering. Should a hardware failure take out the primary instance, the secondary instance will assume normal operations instantly, without requiring a VMotion.
The most significant penalty for this capability is that it requires the same VM footprint to run on both hardware nodes, so if it's a VM with 4GB of RAM, you'll be using 4GB of RAM on each hardware node during normal operation. However, that's small potatoes for running mission-critical virtual servers with this level of redundancy.
Host Profiles is also a fantastic addition, if perhaps overdue. Host Profiles allows admins to build a hardware host system and capture the configuration to be applied to subsequent hardware nodes. Rather than having to manually configure new nodes or even resort to scripted modifications to ESX's internal configuration files, you can now take a single hardware node and propagate its settings to other nodes. In addition, you can check for nodes that may not comply with the profile. This makes the creation and distribution of ESX hosts far simpler, once you've waded through the enormous profile management configuration tree.
While it's hot
Hot Add lets you add not only RAM and CPU but also virtual HBAs and network interface resources to supported VMs on the fly. For instance, you might be able to add another 2GB of RAM and two vCPUs to a Windows Server 2008 instance without even rebooting the box. The operative phrase here is "supported VMs." Hot adds are obviously not supported by most x86 operating systems, but this feature goes a long way toward adapting operating systems to the virtual environment rather than the other way around.
The same can be said for vNetwork Distributed Switch, the new facility to simplify provisioning and administration of VM networks. It allows for the integration of third-party virtual switches, like Cisco's Nexus product, and is a key part of Cisco's Unified Computing initiative.