As of early 2023 ESXi 8.x is the current version of this hypervisor, but many users are quite behind in terms of updating. Partly this may be due to the costs of new licences but also the changes to hardware that 8.x requires. For instance, some CPUs are no longer supported and booting from SD cards or USB keys is also depreciated - the recommended set-up is now to have a RAID 1 pair of 120GB or so SSDs to boot from. Also, there may be third part issues such as the backup software used in the virtual environment.
We have one client who was running 6.5 and wanted to update but only to 7.3, which is a sensible 'jump'. This is a log of what we did and what happened - spoiler - it all worked!
First, as always, read the VM documents and compatibility matrices. If you use VCenter, update that first - this is essential or you might end up painted into a corner.
Then decide how you are going to perform the update. I assume you have already downloaded the ISO for 7.3 and got a suitable licence. If not, then don't worry too much, as you get a 60 day evaluation period to cover that.
If you have Dell servers then using the Virtual media interface in the iDRAC card is an easy option - it allows the ISO to be mounted from a remote PC and joined to the iDRAC and then to set the iDRAC to boot not ESXi but rather the update ISO. This will then run through a wizard and update the v6.5 ESXi on the Dell host.
If you have HP boxes then they can do a similar trick, or you might just use a USB key plugged into the server for the update.
In any case, either vMotion any VMs away from the host or for single host environments, power them all down or suspend them. This includes vvCenter.
Once all is powered down, set the host to reboot and it will then boot from the ISO.
Then it is just a matter of following the wizard. Here is our timeline, which I always think is useful to know how long the process will take in advance. With this low end Dell sever the entire system was updated and back up and working in less than 30 minutes.
Off we go... time = 0 min
Reboot the server
Time = 10 min and the RAM disk has loaded and the server restarts.
Time = 15 mins - update starts for real.
Chose the target drive for the installation - in this case it is the internal dual SD cards.
The warning that this Intel CPU might not be supported in future.
Final warning..
Time = 30 mins, update completed. Note warning about evaluation period.
The ESXi host now shows the updated system.
