Functions
9.2 Enhanced Write Filter (EWF)
SIMATIC IPC427C
Operating Instructions, 04/2009, A5E02414743-01
49
Special features for the use of Enhanced Write Filters (EWF)
● In the event of a power failure, if the EWF is enabled changes made after the boot
sequence on drive C: are lost.
To prevent data loss in the event of a power failure, the use of a USV is recommended.
● You can save the files in the EWF RAM overlay to the Compact Flash card or the hard
disk before you shut down the device. To do so, enter the following command in the
command prompt:
ewfmgr c: -commitanddisable
Then restart the system.
ewfmgr c: -enable
Then restart the system.
Note
When the system is set to automatically adjust the clock for daylight saving time adjustment,
systems without central time management and with activated EWF set the clock forward or
backward by one hour in the daylight saving time or standard time period each time the
system boots.
The reason for this behavior is that Windows Embedded Standard 2009 has a registry entry
that detects if the clock has been adjusted for daylight saving time. Since this file is also
protected against modification by the EWF, the marker is lost during the boot sequence and
the adjustment is made again.
We therefore recommend that you deactivate the automatic adjustment and change the
clock manually.
Procedure:
1. Switch off the EWF filter (ewfmgr c: -commitanddisable) and reboot the system.
2. Deactivate automatic adjustment in the Control Panel. In the Time Zone tab opened with
the menu command Start > Control Panel > Date and Time, remove the check mark from
the "Automatically adjust clock for daylight saving changes" check box.
3. Enable EWF again (ewfmgr c: -enable) and reboot the system.
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