After the announcement made at VMworld about 3 weeks ago, vSphere 5.1 is finally generally available for download and your installation pleasure. Since there are enough posts with aggregated link collections to downloads already and I’m lazy, check this post on yellow-bricks.com for example. The HP custom ESXi ISO for 5.1 containing the latest HP extensions released recently is available for download too.
However, leave any laziness behind and take your time to check the vSphere 5.1 release notes, as these document a huge amount of known issues (with some workarounds):
I hope VMware didn’t rush this release and properly implemented all the nice improvements.
According to the release notes, 5.1 is set to be the last major release to formally support legacy old GuestOS’s such as Windows 3.1/NT/95/98/, RHEL 2.1, OS/2, Novell Netware or Ubuntu 8.*/9.*, which long since ran out of OS support too.
A few of these old OSes are already listed as deprecated for 5.1 in the Compatibility List according to the GuestOS support policy.
The HCL was updated to contain 5.1 info,
while the compatibility matrix has yet to be updated with any 5.1 products (Update: info now available). As usual, you will have to update vCenter first and then the hosts or other depending applications.
I also suppose the new 5.1 VMware Tools are supported even running on 5.0 only clusters too, as it was in previous versions. This might save you an unnecessary reboot later.
It’s time to start up the printer and get really familiar with esxcli, as this will be the primary tool for cli management, especially in case of emergencies where you don’t have access to Powercli or GUI tools. esxcli in combination with the vMA provided vifastpass authentication comes in especially handy.
If you already run Windows Server 2012 VMs (Tech Preview support) on your 5.0 U1 infrastructure, be aware of this significant issue when you upgrade to 5.1:
Snapshots and checkpoints of virtual machines with Windows 8 or Windows Server 2012 do not boot
>Snapshots and checkpoints of virtual machines with Windows 8 or Windows Server 2012 that are taken on a host running ESXi 5.0 Update 1 or ESXi 5.0 P03 will not resume on a host running later versions of ESXi ( ESXi 5.0 Update 2, ESXi 5.1, etc.) and the reverse
>VMotion is prevented between hosts running ESXi 5.0 Update 1 or ESXi 5.0 P03 to and from hosts running later versions of ESXi .