It happened on several R620 with Windows 2012R2. OME System update rebooted the server. It seems that the rebooting was not done through Windows. (asked the OS to reboot)
Windows event log did not log this event. It hit hard on hyper-v. Virtual machines were not properly shut down. Many VMs booted into recovery model when windows came up. This may cause VM disc corruption.
Anyone encountered similar issue? So can someone explain the rebooting process?