I wanted to share with you how I did the upgrade of a stretched vSAN cluster recently.
The steps to upgrade vSAN are as follows:
1: Upgrade the vCenter
2: Replace the Witness node.
3: Update esxi hosts of the vSAN
4: Upgrade the file system
5: Check objects and clean up if required.
Pre-requisites for the upgrade:
1: You will need to register an IP and a fqdn of the new witness node.
2: you will need to download the vSAN witness node for the version you are upgrading do. In most cases this will be the newest vSAN witness appliance. You get this from myvmware.com and then going for vSAN and tools.
3: You should check Skyline and make sure that everything is ok before the upgrade. Don’t start the upgrade on a broken vSAN if you can avoid it.
4: Make sure ntp, fqdn, and such things are working before you start. Make sure you can ping your other nodes (witness and first/second node) with vmkping.
ntp:
Make sure where you have services and that MTUs are set correctly. Keeping in mind here that most people have 9000 there, I only have 1500. This can work for test and such, just make sure it is the same setting on all nodes (and switches etc).
Make sure the switches otherwise are setup and that you have the required networks and that nodes are reachable in the cluster. This here will be a simplified setup because I am doing it nested. I highly recommend reading through VMware documentation and design considerations for 2 node clusters. You can find that documentation here.
For prequisites and upgrade of vCenter please see here (and here for the pre-reqs for the upgrade).
After this we can get started on the rest of the steps.