I have two DL380 servers. One is a G6 and the other a G7 running ESXi 4.1, in vcenter. This morning at 0708 both host shutdown. Upon arrival at the site, both hosts had power and just needed to be powered on. No other servers were shut down or rebooted in the rack. The servers are also configured to turn on when power is applied, but did not do so. They are also attached to a UPS. The UPS log showed two low voltage events shortly before the servers went down, each was about 6 seconds.
We believe the UPS is faulty, but it does not indicate so in our monitoring software.
What logs can I look at on the ESXi servers to get any information on what may have happened?