Helient Systems :

by Jamie Engelhard, Chief Technology Officer

This is a reminder that Daylight Saving Time will begin at 2:00 AM on Sunday, March 11^th. This semiannual time change can cause major problems with VDI environments such as machine registration issues, session disconnects, and group policy failures. Whether using Citrix Provisioning Services, Citrix Machine Creation Services, or VMware Horizon View Linked/Instant Clones, non-persistent machines revert to the base image every time they are rebooted. After the upcoming change to Daylight Saving Time, the clock on these machines will be off by 1 hour every time they are rebooted until the base image is updated to the correct time. The effect of this is that the machine’s system clock will not match the time in the Windows Domain for a brief period of time after a reboot. This can lead to issues obtaining IP addresses and authenticating with Domain Controllers, which can cause a variety of problems within the desktop and user environment.

Some of these side-effects might include:

• Errors applying machine Group Policies
• Errors logging into the domain
• Login scripts not running
• Errors acquiring / renewing IP addresses from DHCP
• Communication issues with virtual desktop agents
• Failed user connections
• Unregistered machines

After the machine has been running for a period of time, the clock will adjust, domain authentication will succeed, and machine policies will apply (assuming background processing of Group Policy is enabled in your domain) but it is the period immediately after a restart which can be problematic and cause unusual behavior and outright service failures. Please be aware of this issue and make plans to update your base image, as this is the only way to fully remedy this problem.

Below are some links for further reference on both VMware Horizon and XenDesktop:

• http://support.citrix.com/article/CTX200058 – Provisioning Services and Daylight-Saving Time
• https://kb.vmware.com/s/article/2074301 – The time stamp on a snapshot image does not update automatically in VMware Horizon View (2074301)

The severity and impact of these issues depends on many factors within the environment, such as DHCP lease times and whether Group Policy provides critical settings to machines at boot time, without which they will not register or function correctly. Many environments can continue to run with the initial clock skew and report no issues. However, the only way to guarantee that none of these issues occurs is to update the base image after the time change to reflect the current and correct time.

Please plan accordingly to update your image(s) and, at the very least, carefully test your VDI systems on Sunday morning after the time change to make sure your business is not interrupted on Monday. If you have any questions or need assistance during this transition, please contact us at service@helient.com.