Unresponsive Servers due to DST and an unsupported registry key

Hi, David here to tell you about a thorny little problem that a few of our customers have run into during their testing for the upcoming Daylight Saving Time changes. For reference, the US enters DST this weekend, and parts of Europe enter DST on March 25th. (For a list of all the various Daylight Saving Time changes, click here)

What you need to know

If you have the following registry key implemented on any Windows systems, and your system clock is running faster than your CMOS clock, that computer will become unresponsive at the DST change. This unresponsiveness will persist until the CMOS clock catches up with the DST changeover time. For example, if the CMOS clock is set to 3/11/2012 6:55 AM UTC and the OS time is set to 3/11/2012 1:59 AM EST, when the system clock reaches 2:00 AM EST, the CPU will spike to 100%, and will remain pegged for 4 minutes until the CMOS clock reaches 7:00 AM UTC.

Key: HKEY_LOCAL_MACHINESystemCurrentControlSetControlTimeZoneInformation
Value: RealTimeIsUniversal
Data: 0x1 (default: 0x0)

We recommend the following steps:

1. Don’t use the undocumented and unsupported RealTimeIsUniversal registry key! If you have it set, delete it and reboot that computer. Make sure it doesn’t return via automation, like Startup Scripts or Group Policy Preferences

2. Check CMOS clocks on your systems and make sure that they are set to the correct time (yes, we know this requires a reboot).

See this KB article:

268725 – System may be unresponsive around Daylight Saving Time (DST) change when RealTimeIsUniversal is Set


David “What’s a TARDIS?” Beach