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// Tales from software development

Windows Server 2003: UPS protected server drops off network

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I have a small server running WIndows Server 2003 and protected by an APC BackUPS CS 500 UPS. The server runs headless and is only occasionally accessed using RDP.

Recently the server has started disappearing off the network. It’ll run OK for a few days but then can’t be located on the network although it’s still powered up. I assumed that it was blue screening or something similar but because it runs headless it was impossible to know. Powering it off and on always brought it back on line and the event logs didn’t show anything unusual. In fact, the event logs seemed to indicate that the server was operating normally when it became inaccessible.

The first rule of problem diagnosis: what’s been changed ? Nothing. Sure ? Hmmm, well I did recently install new drivers for the server’s two NICs…

I spent an hour yesterday trying to work out if there was anything wrong with the way the server was configured that might cause the problem. Eventually, I noticed in the Control Panel Device Manager that the active NIC was configured with the Allow the computer to turn off this device to save power setting. Normally, I’d only expect to see this setting set on a laptop so why was it set on by default on this server ?

My suspicion is that it’s because this server is attached to a USB enabled UPS. Windows Server 2003 supports this type of UPS by treating it as a battery based power supply in exactly the same way as Windows handles laptop power management.

I haven’t proved this yet but I strongly suspect that the USB enabled UPS has fooled Windows into thinking that this is a laptop type machine and so when I reinstalled the NIC drivers the Allow the computer to turn off this device to save power setting has been set on by default as would be appropriate for a laptop. 

Typcally, I get a couple a couple of brown outs a week where the voltage drops enough for the UPS to kick in. I’m guessing that as soon as Windows 2003 identifies that it’s running on battery power the NIC is powered off because of the Allow the computer to turn off this device to save power setting and the server ‘disappears’ off the network.

I’ve changed the Allow the computer to turn off this device to save power s setting so now I need to give it a couple of weeks to see if the problem goes away.

The other change I’ve made is to configure the two Alarm Action settings on the Alarms tab of the Power Management control panel applet. Each one now calls a task that executes a batch file that writes a date and time stamped message into a log file and also issues a syslog broadcasts with the message. The first alarm, the Low Battery alarm, simply logs the fact that the alarm has been triggered. The second, the Critical Battery alarm, logs the alarm and shuts the server down.

Broadcasting the power alarms seems like a good idea anyway but logging the alarms should help to confirm if the problem has now been resolved. 

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Written by Sea Monkey

January 14, 2010 at 8:00 am

Posted in Hardware

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