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It seems that the only method for an NMC to restart a server after it has been shut down is to cut then restore power to it. That is, for the UPS to signal a server to restart, it must switch itself to the "OFF" state, and then switch itself back "ON". For a single server, the configuration to accomplish this is straightforward. However, for multiple sequenced servers I cannot seem to find a configuration where restart of all servers occurs reliably.
Consider this sequence from the PowerChute NS online help:
Long Outage Works Fine
If the outage is long enough for the UPS to shutdown and enter its OFF state, there is no problem. When the mains power is restored, the UPS turns itself back ON, the servers see power again, and they heed the return of power as their signal to restart.
Short Outage Leaves Some Servers Off Indefinitely
Now consider the case where mains power is restored after Server B Shutdown, but before Server A Shutdown. The result is as follows:
- Server A - Remains Powered
- Server B - Off Indefinitely
- Server C - Off Indefinitely
This is because the UPS never shut down to the OFF state. Therefore the UPS cannot signal Server B and Server C to restart by turning back ON.
(I just confirmed the behavior of both the long and short outage cases with the NMC2 v6.0.6 and PowerChute NS configured on two servers.)
What It Seems Like Should Happen
If the following conditions are true:
- mains power is restored,
- and any PowerChute clients have already started shutdown
then the UPS following should do the following:
- initiate an immediate shutdown of all servers
- turn itself OFF
- turn itself ON again
(The FAQ for NUT covers this case and confirms that that should be the prescribed UPS behavior: http://www.networkupstools.org/docs/FAQ.html#_i_8217_m_facing_a_power_race)
On my configuration, though, this is not what happens. Is there a configuration that restarts Server B and Server C even if mains power is restored after Server B Shutdown, but before Server A Shutdown?
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