12 Troubleshooting flush for each write operation and should solve the problem in any case, but has a severe write performance penalty. Providing a value of 0 for [b] is treated as an infinite flush interval, effectively disabling this workaround. Removing the extra data key by specifying no value for [b] has the same effect. 12.2.2 Responding to guest IDE/SATA flush requests If desired, the virtual disk images can be flushed when the guest issues the IDE FLUSH CACHE command. Normally these requests are ignored for improved performance. The parameters below are only accepted for disk drives. They must not be set for DVD drives. To enable flushing for IDE disks, issue the following command: VBoxManage setextradata "VM name" "VBoxInternal/Devices/piix3ide/0/LUN#[x]/Config/IgnoreFlush" 0 The value [x] that selects the disk is 0 for the master device on the first channel, 1 for the slave device on the first channel, 2 for the master device on the second channel or 3 for the master device on the second channel. To enable flushing for SATA disks, issue the following command: VBoxManage setextradata "VM name" "VBoxInternal/Devices/ahci/0/LUN#[x]/Config/IgnoreFlush" 0 The value [x] that selects the disk can be a value between 0 and 29. Note that this doesn’t affect the flushes performed according to the configuration described in chapter 12.2.1, Guest shows IDE/SATA errors for file-based images on slow host file system, page 168. Restoring the default of ignoring flush commands is possible by setting the value to 1 or by removing the key. 12.2.3 Poor performance caused by host power management On some hardware platforms and operating systems, virtualization peformance is negatively affected by host CPU power management. The symptoms may be choppy audio in the guest or erratic guest clock behavior. Some of the problems may be caused by firmware and/or host operating system bugs. There- fore, updating the firmware and applying operating systems fixes is recommended. For optimal virtualization performance, the C1E power state support in the system’s BIOS should be disabled, if such a setting is available (not all systems support the C1E power state). Disabling other power management settings may also improve performance. However, a balance between performance and power consumption must always be considered. 12.2.4 GUI: 2D Video Acceleration option is grayed out To use 2D Video Acceleration within VirtualBox, your host’s video card should support certain OpenGL extensions. On startup, VirtualBox checks for those extensions, and, if the test fails, this option is silently grayed out. To find out why it has failed, you can manually execute the following command: VBoxTestOGL --log "log_file_name" --test 2D It will list the required OpenGL extensions one by one and will show you which one failed the test. This usually means that you are running an outdated or misconfigured OpenGL driver on your host. It can also mean that your video chip is lacking required functionality. 169