PDU Failures and Life Span of PDU's

[Anonymous user]

Hello. What are the typical lifespans of Switched Rack and/or Basic Rack PDU's? Are error messages on the display indicative of needing to replace the PDU? My company wants to make sure that our PDU's can still allow power to pass through them even if the display indicates there is an error.

Is there a way to know the PDU will fail or does it just suddenly stop working?

Thank you.

[Anonymous user]

Speaking as a customer, I've had well over 100 units over the years, starting with the AP9210 (caution - well-known security issue) through to the current AP790x. I've never had one fail in a manner that dropped the load. The management board in these is actually separate from the piece that controls the power relays, communicating via a serial bus. Unless the management board sends a command in the correct format to the relay board, the relay board will ignore the management board.

That's for units which are powered on when the management board fails. The default state for the relays on the relay board is off, so if the management card doesn't tell them to turn on the load, unplugging the PDU from its power source and reconnecting it will not turn on the outlets if the management board isn't working.

The power path from the input plug to the outlets is pretty simple and I'd expect very few failures there. There seem to be redundant power supplies in the modern PDUs for powering the relays (the device status shows a primary and decondary power supply) so I wouldn't expect the relays to drop out from a power supply failure.

Aside from sudden catastrophic failure, the first thing you'll normally see are emails / log messages / traps (depending on what you configured) reporting warmstarts on the management card. This can indicate a developing hardware problem, or it can be a software problem. The newer units try to ping their default gateway and if it doesn't respond for 10 minutes or so, the management board decides it has a network problem and reboots to try to fix it. Some older software could also do a panic reboot when receiving malformed packets from an attacker. Later software corrected this. None of these things affect the loads plugged into the unit.

[Anonymous user]

How do I determine if my PDU has a secondary power supply? I have a bunch of AP7941 PDU's, a few AP8941's, and a few AP7911A's. It doesn't seem to clearly indicate in the online documentation if they have secondary power supplies.

Angela states "on a switched rack PDU, usually if the NMC cannot boot or something else is wrong with it, the PDU will not output power due to the design and the relay boards" Being that a majority of our PDU's are switched rack PDU's does this mean that the PDU would not be able to pass power through it if the NMC has a problem hardware or software wise?

[BillP · Accepted solution]

i believe we say PDUs typically have a 6 year lifespan. also, in addition to what terry mentioned, both metered and switch rack pdus have a primary and secondary power supply to help avoid any failures that would cause the relays to fail closed and turn off the output on the PDU. on a metered rack PDU, if there is an NMC failure/issue, the PDU will still pass power. on a switched rack PDU, usually if the NMC cannot boot or something else is wrong with it, the PDU will not output power due to the design and the relay boards, etc. not all competitors have a secondary power supply so if either fails, you still have a backup to avoid any dropped loads. the built in management card provides detailed alarms, logs, etc to help monitor the device and your load current at a minimum.

[Anonymous user · Accepted solution]

If you access the PDU via the console or Telnet interface, the dual power supply status shows up in the device manager menu tree (Device Manager / Power Supply Status). I don't see it in the web interface on the PDU.

I believe Angela and I are both saying the same thing - that if the management card in the PDU fails, the loads will remain in their current state until input power is disconnected from the PDU. At that point, all outlets will be off and remain off until the management card successfully boots, any configured turn-on delays expire, and so on. If the management card doesn't boot for some reason, all outlets will remain off.

[BillP · Accepted solution]

yes, via the web UI you will only get a notification of when there is a fault with a power supply. in the telnet/ssh/local console, you can verify their status all of the time whether they are in a normal or fault state.

because a switched rack PDU offers outlet control and relays need to be open or closed to pass the power to the outlets, if the NMC and PDU cannot fully boot up, the PDU itself will not be able to operate the relays if there is an NMC hardware problem that prevents PDU booting. on a metered PDU it works differently due to the lack of individual outlet control so NMC fault or not, the PDU will still pass power.