Use of hibernation may cause slower starts and resumes when BitLocker Drive Encryption is enabled

Applies to: Windows 7 EnterpriseWindows 7 ProfessionalWindows Server 2008 R2 Datacenter

Symptoms


When BitLocker Drive Encryption is used to encrypt the operating system volumes, after the first resume from hibernation, the later resumes from Hibernate and the next system restart may be slower. This includes resumes from Hibernate, restarts, and shutdowns that are followed by turning on the computer. This slowdown happens because the firmware clears the system’s RAM during the restart process. Operating systems that do not use Hibernate do not encounter this problem.

Cause


During restart, BitLocker Drive Encryption configures the firmware to clear memory on the next restart if the system is shut down unexpectedly. During resume from hibernation, BitLocker configures the firmware to clear memory on the later restart, regardless of the cause of shutdown. This issue begins after the first resume from hibernation, continues across Hibernate cycles, and ends after the slow restart that follows a shutdown or a restart. Therefore, on a restart that follows a resume from Hibernate, as instructed by BitLocker, the firmware clears the memory during the restart process. The delay for users while memory is cleared varies, and this delay depends on the physical configuration of the system and the memory size.

Resolution


We recommend that you disable Hibernation and use system shutdown instead.

Additionally, some platform manufacturers may have implemented BIOS optimizations to improve the memory-clearing performance. We also recommend that you install the latest BIOS update from the computer manufacturer, if an update is available.

More Information


For more information about how to disable hibernation, click the following article number to view the article in the Microsoft Knowledge Base:
920730 How to disable and re-enable hibernation on a computer that is running Windows
For more information about BitLocker Drive Encryption, visit the following Microsoft TechNet website: