Hi, Hassan.
Here it is very well explained in my opinion: Updating Firmware in vSAN Clusters
However, this is my hand-made step by step.
Pre-checks:
1 - Verify drivers versions (Determining Network/Storage firmware and driver version in ESXi 4.x and later (1027206) | VMware KB)
2 - Download the drivers and firmware files. Here is a useful link to get drivers download links https://hcl.captain-vsan.com/index.php
3 - To upgrade the firmware you may need to install a Vendor Tool to do it from vSphere, or directly upgrade from the One View console, or whatever the vendor IPMI console is.
4 - Make sure the vSAN cluster have enough capacity to keep, at least, 25% free when a host enters maintenance mode.
5 - Make sure you have an useful baseline created and attached to ESXi hosts.
Time for action:
1 - Import the drivers / firmware files into VUM and add them to the baseline.
2 - Enter the ESXi into maintenance mode. (You may use Ensure Accesibility to keep the data safe, but it really depends in each scenario and customer need)
3 - Remediate the ESXi
4 - Repeat 2 and 3 for each ESXi in the cluster.
Post update:
1 - Make sure to run a vSAN Skyline Health check and verify is in order.
2 - You may want to check manually if the drivers applied correctly in each ESXi. You can access this info in vSAN Skyline health tab, or with ESXCLI commands for each ESXi.
