Write Filter Support

  • Article

5/4/2012

Many Windows Embedded operating systems include a Write Filter feature that enables writes to disk to be redirected to RAM or a temporary volume. The image on the device is then consistently persisted and every session on that device, following a restart, is the same. Device Manager 2011 supports the following types of write filters:

If you receive a device from the device manufacturer with write filters disabled, use the FBWF Manager or EWF Manager command line tools to enable the write filters for the first time. For more information about FBWF Manager, see FBWF Manager on MSDN. For more information about EWF Manager, see EWF Manager Commands on MSDN. For more information about how to use a command-line tool with Configuration Manager, see Run Command Line in Configuration Manager Help.

You can use Device Manager 2011 to efficiently update software on managed client devices that have write filters enabled. The following list shows the three ways you can disable and then restore write filters in Device Manager 2011 during a software deployment:

  • Create an advertisement that disables and restores write filters using the New Advertisement with Write Filter Handling Wizard.
    To deploy a single package to a collection of devices that use write filters, use the New Advertisement with Write Filter Handling Wizard in the Configuration Manager console. The wizard automatically creates a task sequence from the selected package that disables write filters, performs the service actions in the package, and then restores the write filters.
  • Create an advertisement that disables and restores write filters using a custom script.
    To use a custom script to create an advertisement that disables and then restores write filters, you must use the EDM_WriteFilterAdvertisementFormatter WMI class. For more information, see EDM_WriteFilterAdvertisementFormatter on MSDN.
  • Create a custom task sequence that disables and restores write filters.
    To perform a set of updates in a specific order with multiple service actions in the package, create a custom task sequence. Device Manager 2011 adds extensions that disable and restore write filters to the Task Sequence Editor in Configuration Manager console.

Note

Using custom scripts in packages to disable and restore write filters is optional. If you decide to use custom scripts, use Visual Basic Script and the EDM_WriteFilterAdvertisementFormatter WMI class. Modify the created task sequence to disable write filters, install the software package for the input package/program combination, and then restore write filters. You can also add code to create an advertisement from this task sequence.

During the software deployment process, Device Manager 2011 uses the following basic procedure. After Device Manager 2011 detects write filters, it saves configuration information. If Hibernate Once Resume Many (HORM) is used on the device, HORM is deactivated. The device displays the countdown that you set in Configuration Manager to warn users that the device is going to be updated, and then disables write filters. Device Manager 2011 restarts the device from the operating system at least once and an additional restart is performed for each drive protected by EWF in RAM Reg mode. The device is now locked and only users who have Administrator credentials can log on to the device.

Next, the task sequence restarts. If the advertisement is mandatory, the countdown that you set in Configuration Manager will restart from the beginning after the task sequence restarts, and then the software deployment will begin. Otherwise, the software deployment will begin immediately. When the software deployment is completed, Device Manager 2011 restores the write filters. If HORM was previously used on the device, Device Manager 2011 restores HORM. Device Manager 2011 restarts the device operating system. If HORM was not used in the past, the process is completed. If HORM has been restored, the device starts hibernation and will restart from the hibernation file when it is needed.

Note

HORM remains disabled on both 32-bit and 64-bit devices running Windows Embedded Standard 7 with Enhanced Write Filter (EWF) in RAM Reg mode. You can manually reactivate HORM after the advertisement completes successfully. If EWF is using the default optimization option (Optimal Performance), this issue does not occur.

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