What happen to UPS when power is restored while on graceful shutdown delay.

[Anonymous user]

Hi all,

I have a SMART UPS XL 3000 with a NMC. I am actually configuring PCNS in a VMware environnement for graceful shutdown in case of power failure. Everything is fin for the moment, but there is still a scenario that I'd like to explore to be certain that my configuration is bulletproof. So I configured PCNS to shutdown(halt) the UPS when the shutdown processed is completed. This way, when power would come backup, UPS would pop up again, sending power to my server that will power on again right after this. Here is the situation. Let say the power goes off, the shutdown sequence is initiated by PCNS, my PCNS server is shutdown, the UPS is waiting his graceful delay, then the powered is restored before the UPS has halted. Then, since shutdown is initiated, the UPS should halt enven if power is restored (I guess), but what after that? The UPS is configured to restart as soon as the power goes on (with minimum battery power of course), but what if is was the power is already back when the UPS halt? Will it pop up back automatically as it sees that there is power or will it wait a human action to goes back online and start the servers? If it stays off, what would be the best solution to get rid of this possible situation where the infrastrcuture would stay down after a power outage?

Thank you very much

[BillP]

Hello,

1. If the power is restored to the UPS while the UPS itself is beginning its graceful shutdown and reboot process, the UPS will complete its graceful shutdown and reboot cycle and then turn back on since it will see that AC power is already back at the end of the process. This includes cutting power temporarily to the devices which if their BIOS is set correctly (if applicable), they'd come back on and reboot themselves.
2. If the power is restored to the UPS and the UPS itself has not started any graceful shutdown or reboot processes, but your PCNS clients have and are shutting down, I believe either the user will need to manually reboot the UPS (so that the PCNS and computers see an interruption in power) or go and manually turn things on that have turned off (like if only one client has shut down based on your PCNS settings but others have not). You'll have to do this because PC's that are typically able to reboot after this need to see the interruption in AC power to trigger a reboot (based on those BIOS settings I mentioned). If the UPS is constantly outputting power via its own battery or while the UPS is online, this interruption does not happen so the devices stay off.

If scenario 2 happens, a Switched Rack PDU (or if your UPS is newer and contains Switched Outlet groups) may help to facilitate this interruption of power rather than rebooting the entire UPS. If your UPS does have switched outlet groups, it may be wise to arrange devices connected based on how they will shutdown so that for instance, you may be able to just reboot one outlet group with clients that have already shutdown in scenario 2 rather than ALL clients or attached devices (if not using PCNS).

Bill P. - did I miss anything here? Or anything to add?

[BillP]

Hi,

If you have PCNS configured to send shutdown signal to the NMC/UPS then it will send that signal at the same time it commands the OS down. The UPS will wait any delays you have configured and then power down. If AC is restored to the UPS after PCNS has sent the power down signal the UPS will still power down and either wait any power up delay you have configured or if no delay has been configured will restore power to the load once the power down cycle is completed.

I recommend that you

1 - Include UPS power down delay to allow the load enough time to power down before the UPS cuts AC.

2 - Make sure that when power is restored the battery can sustain the load at least long enough to have it power down again properly. You can do this by either configuring a power up delay (let battery charge up before restoring power) or having the load shutdown before battery is drain to the point that it cannot sustain the load for the needed power up and shutdown cycles.

If you provide the exact model Smart-UPS 3000, the NMC model and firmware, the version of PCNS you are installing I can provide an example.

[Anonymous user]

Hi,

I have one last thing I'd like to add (but your answer is pretty much convers everything). I only have a single PCNS device wich is a VMWare vMA. It is this machine that covers the process of shutting down all my VM, not PCNS itself. PCNS only covers the shutting down of my three VMware host. Then, the UPS is shutdown after the delay. Since I only have one PCNS device and the software is configured to shutdown the UPS, I am right to believe that even if power is restored during shutdown process of PCNS, since shutdown process HAS BEEN initiated by PCNS and it will pursue until completion so it should shutdown my UPS even if power is restored before the part where PCNS tell the UPS to actally shutdown?

Thank you very much

[BillP · Accepted solution]

Yes. Once shutdown has started it will complete the process even if AC is restored during that time.

[Anonymous user]

Thanks again for your time

Simon