I was just testing the new patches on a couple of servers when I noticed that when I pressed “remediate” the first patch(ESX350-200802403-BG) was installed without the ESX host going into maintenance mode. When the second patch(ESX350-200802409-BG) was installed the server went into maintenance mode. According to the VUM Documentation(vi3_vum_10_admin_guide.pdf) the server should always go into maintenance mode before installing the patches:
Update Manager puts ESX Server in maintenance mode before applying updates. Virtual machines cannot continue to run when an ESX Server is in maintenance mode. To ensure a consistent user experience, Update Manager migrates virtual machines to other ESX Server hosts before the server being remediated is put in maintenance mode.
I can imagine this happens because the system impact of the first patch is “No VM Shutdown & No Host Reboot” and for the second patch it is “VM Shutdown & Host Reboot”. Anyway, it would be a nice addition if one could choose to always enter maintenance mode before applying patches. It definitely gives me a more save feeling.