User tasks
4.6 Managing the Enhanced Write Filter
SIMATIC IPC427C Bundles, SIMATIC HMI IPC477C Bundles
Manual, 07/2009, A5E02280126-02
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4.6 Managing the Enhanced Write Filter
Definition
The Enhanced Write Filter (EWF) is a Windows Embedded utility for protecting a
CompactFlash card. CompactFlash cards allow a limited number of write accesses.
When the Enhanced Write Filter is enabled, Windows Embedded writes no data to the
CompactFlash card. Instead, the file writes are kept in virtual memory.
Functionality
No difference is apparent to you when you view file contents. File information appears the
same whether it actually resides on the CompactFlash card or in virtual memory.
The difference in file storage is evident when you reboot the computer or it loses power.
All data in virtual memory is lost, and the computer restarts with the file contents of the
CompactFlash card.
You can manage the EWF to maintain data that must be retained after a reboot.
If you disable the EWF, all file writes go to the CompactFlash card. This does result in the
persistence of all data after a power loss; however, it causes the most stress over time to the
CompactFlash card.
NOTICE
The Enhanced Write Filter default setting of the D:\ and C:\ drive on the
SIMATIC Embedded Bundles is "Disabled". To protect the CompactFlash card from early
failure due to continuous writes, enable the EWF for the C:\ drive after you have finished
the development of applications on the C:\ drive.
You can also commit all data that is stored in virtual memory to the CompactFlash card at
any point in time, using one of the following commands:
● commit: The "commit" EWF command writes all data that has accumulated in virtual
memory at that moment in time to the CompactFlash card. The CompactFlash card is not
disabled.
● commitanddisable: The "commitanddisable" EWF command disables the EWF and then
writes all data that has accumulated in virtual memory to the CompactFlash card.
Typically, this command is followed by an enable command to once again protect the
CompactFlash card.
To use the Enhanced Write Filter manager, follow these steps:
1. Open a command prompt window.
2. Enter "ewfmgr" followed by a drive designation and a command as illustrated.
3. Reboot the computer for the command to take effect.
NOTICE
After you enter commands, you must reboot the computer for the ewfmgr commands to
take effect.
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