I went into the BIOS of each of the ESXi hosts and enabled Wake-On-LAN. I placed both of them into a cluster and enabled DPM. I then attempted to place one of the hosts into standby mode. The vCenter client complained with the following message:
vCenter has determined that it cannot resume host lab1.example.com from standby; therefore, the enter standby task was stopped. Confirm that IPMI/iLO is correctly configured for host lab1.example.com. Or, configure vCenter to use Wake-On-LAN, ensuring there are at least two or more hosts in the cluster, and try the task again.
That last line really bugs me because there is no WOL-specific configuration options in vCenter. After a little digging around (RTFM) I read that vCenter must be able to send the WOL "magic packet" to a physical NIC where vMotion is enabled. I had not yet enabled vMotion on these two lab hosts!
After enabling vMotion on my hosts, I was able to successfully place them into standby mode. Even more importantly was the fact that vCenter could wake them back up again.
I observed one other quirky behavior with DPM. When attempting to manually power-on the sleeping host, vCenter's "please wait" message reads:
Waiting for host to power off before trying to power it on
This comes AFTER I get confirmation that the "Host is in Standby Mode". It could be that vCenter still isn't sure if the machine is fully powered-off just yet, so it's waiting an arbitrary amount of time before sending the WOL packets to my host. I'll have to play with it a little more and see if vCenter gives the same misleading "please wait" message when powering-on a host that has been sleeping for a while.
