We have several vsan streched cluster (6.5u2 & 6.7u2) for which we plan a full site maintenance and I would have liked to have your opinion on the modus operandi that we plan to apply :
Does that seem right ?
I especially have a doubt about the maintenance mode to use, ensure accessibility or no data migration ?
Do you have any data that is FTT=0 or just with local protection (e.g. PFTT=0,SFTT=1)? If you do and these need to remain accessible during the maintenance then I would advise moving these first (change the site in the Storage Policy and reapply it).
Other than that, your plan looks fine - use Ensure Accessibility option, No Action is used more for activities such as physically moving a whole cluster or incoming power outage (and all the data should ideally be cold).
we did not disable HA and DRS but instead created a host group "maint-hosts" and vm group "ALL VMs"
then activated a rule so that ALL VMs must not run on maint-hosts.
now let DRS do its job, and then it is much easier (faster) to bring the vsan "main-hosts" into maintenance mode with "ensure accessiblity"
when you make them exit maintenance mode again, do so quickly one after another, so that no re-placement of components would start (you raised the delay timer anyway...)
only disable or delete the "maint-rule" after you are sure there is no more data resync going on