The system needs to reboot for a configuration change to take effect.

BillP · ‎2021-06-27

I have a AP8930 PDU and am changing the IP number. It says the system needs to reboot for a configuration change to take effect. If I reboot it, will it kill the outlets on the PDU or just reboot the interface?

I can't seem to find a manual for this particular PDU. Does anyone have a link to one?

Terry_Kennedy_apc · ‎2021-06-27

The hysteresis setting was introduced to prevent the problem of a unit continually sending out new email alerts. Say you have a threshold of 75 degrees. The temperature goes above 75, you get an "alarm" message. It goes back to 75, you get an "alarm cleared" message. If the temperature is fluctuating slightly right around the alarm threshold, you can get many of these messages. With hysteresis, the temperature needs to drop back down by the number of hysteresis degrees (for example, to 73 degrees if you set it to 2 degrees) before the unit considers the alarm cleared. Normally the unit will send out "reminder" messages if a violation still exists. You can tune the frequency and delay of those messages as well.

Technical point: As the unit allows temperatures to be set in either degrees C or degrees F, and the actual values read from the probe are voltages that need to be converted to digital numbers, there is a bit of unavoidable "slop" in the conversion process. I normally suggest adding 1 degree F to whatever you think the hysteresis value should be, to avoid nuisance messages.

See Answer In Context

BillP · ‎2021-06-27

Hi Bob,

On any of these APC Rack PDUs, under normal circumstances rebooting the management interface will not affect the outlets or cause them to reboot. I was under the impression as well if you log out or your session expires (and no other users are logged in), it will also automatically do the reboot for you to apply the setting rather than you needing to specifically command it to reboot.

Side note: I would only urge caution to any user coming across this post that if you were going to reboot but your Rack PDU has concerning alarms like lost internal communication alarms because then in these rare potential fault scenarios, the outlets may reboot depending on what the failure is.

Try this link for all the documentation on this PDU: http://www.apc.com/shop/us/en/products/Rack-PDU-2G-Switched-ZeroU-20A-100-120V-24-5-20R/P-AP8930#doc... (you may need to scroll down a little bit and specifically click on the documentation tab to see the documents listed)

BillP · ‎2021-06-27

I appreciate you help and information.

BillP · ‎2021-06-27

So then clicking the "Apply" button doesn't reboot it? I'll look in the documentation on how to reboot it.

If I can, you seem knowledgeable about these things, we have a temperature sensor plugged into this unit.

It is in a small room and the temperature swings from 72-77 over the cooling cycle. We kept getting alarms

for high temperature so I adjusted the set point on the alarm and moved the sensor away from the back of a

server that had been installed. Can you explain to me in simple terms what the Hysteresis is and if I need a small number

or big number? My assumption was that it was like giving me extra time for the temperature to come down so I could avoid

the constant alarms we were getting.

Max (Critical):	°F [32 to 140]
High (Warning):	°F [32 to 140]
Hysteresis:	°F [0 to 18]
Alarm Generation:	Enable

BillP · ‎2021-06-27

Hi Bob,

Correct, you have to specifically give a reboot command. I think also if it has pending changes, when the last user logs off the system, it will reboot after the session ends.

To command a reboot via the command line, you can issue the reboot command and follow the prompts to confirm that. Though the web UI, go to Control->Network->Reset/Reboot and then the radio button defaults to the correct option - "Reboot Management Interface." Then, apply that, which I think it asks you to confirm and you click Apply a second time. Then, the reboot will happen and it takes about 20-30 seconds usually.

On your other question, hysteresis is like a buffer. It is the difference between the particular threshold violation and the clearing point. I usually suggest anything between 3-5º typically. I think you have the right idea of what it is for but maybe you need to set it to 5 or 6º if the temperature variation isn't something you can tighten up or avoid with cooling adjustments, like you did with moving it.

Terry_Kennedy_apc · ‎2021-06-27

The hysteresis setting was introduced to prevent the problem of a unit continually sending out new email alerts. Say you have a threshold of 75 degrees. The temperature goes above 75, you get an "alarm" message. It goes back to 75, you get an "alarm cleared" message. If the temperature is fluctuating slightly right around the alarm threshold, you can get many of these messages. With hysteresis, the temperature needs to drop back down by the number of hysteresis degrees (for example, to 73 degrees if you set it to 2 degrees) before the unit considers the alarm cleared. Normally the unit will send out "reminder" messages if a violation still exists. You can tune the frequency and delay of those messages as well.

Technical point: As the unit allows temperatures to be set in either degrees C or degrees F, and the actual values read from the probe are voltages that need to be converted to digital numbers, there is a bit of unavoidable "slop" in the conversion process. I normally suggest adding 1 degree F to whatever you think the hysteresis value should be, to avoid nuisance messages.