How to update ESXi correctly?

Question

VMware

Colleagues, hello.

There is ESXi 5.5, I want to upgrade it to 6.5.
There are three DAS storages, one of them has ESXi installed. After reading, I see that you can update directly, for example from a CD-ROM (will offer an update option)
Does anyone have experience? Can something break in the process?
And yes, this still torments the question - ESXi 5.5 had a custom image, added drivers for the RAID controller. Updated later.
So, do I need to sew drivers into a new image?

Answer 1

You can update from a CD, from a flash drive, from iKVM/iLO/iDRAC, if available.
A boot image is made, firewood is added, if necessary.
If you need to boot from real media, media is prepared
Boot from image or media
The installer asks "Upgrade boom or what?"
Updates
Once Upon a Time:
During the update process, on one of the hosts, the partition with the machine data itself disappeared, as if I had chosen not to upgrade, but to install on a new one. I had to restore the markup with the generation of new ids, it's good that ESXi turned out to be smart enough for this :DDD otherwise it already calculated the time required to deploy the backup :DDD
One more host needs to be updated, somehow scary ... :)
As for sewing firewood on RAID - I sewed it on 6.0 to the same place where I sewed it on 5.5

Answer 2

It can break. I've seen issues when trying to upgrade from 5.5 to 6.0 on IBM blades and Gen9 proliants. In the first case, it was not possible to treat it in any way, I had to stay at 5.5, in the second case I had to rearrange it completely and roll up component updates by hand - some kind of rake with Intel CIM, and after updating ESXi fell into PSOD at boot.
In general, problems can lie in wait for you with any change in the configuration of systems or infrastructure :-) Therefore, it is considered good practice in Change Management to think over a "plan B" in case something goes wrong :-) That is, options or workarounds problems, or a rollback to a previous state. In this sense, ESXi has the ability to roll back to the previous state by pressing Shift-R at boot (it suggests there before starting to boot). So even if after the update it doesn't work for you - reboot, press Shift-R and return to 5.5.