10 | More about MC6 and AS6?
STOBER
60
05/2018 | ID 442461.04
10.1.3
Measures for data security
Control systems are very frequently used in areas where a controlled shutdown is not possible.
In particular, if control systems are based on PC technology and a standard operating system is
being used, the file system is at risk of getting damaged. The only safe method of protecting a
Windows file system is to use an uninterruptible power supply (UPS). If the power supply cuts
out, these systems provide the power required for shutdown. In addition, they inform the
operating system through a potential input or a serial interface so that a shutdown can be
initiated immediately.
Disadvantages of this hardware solution include increased costs for the additional hardware. In
addition, UPS systems usually store their energy in bundles of multiple batteries with only a
limited service life, thereby necessarily leading to increased maintenance effort.
Pure software solutions cannot prevent damage to the file system when the power is lost.
However, suitable measures reduce the frequency of this occurring or facilitate repair.
Furthermore, no effort or expenses are incurred for additional hardware and maintenance.
A description of measures taken on STOBER systems to increase the safety of the file system
and of the data contained in it in the event of a power failure is presented below.
First shut down, then switch off
If the MC6 motion controller is switched off while the software is writing a file to the CFast
memory device, this file will be damaged in most cases.
As a rule, controller software writes to the memory device independently at intervals of a few
seconds. This means there is a high probability damage will be caused when the device is
switched off while software is running. However, various measures have been taken to minimize
the occurrence of such conditions.
EWF Manager
The standard measure for protecting an application in a NTFS-based Windows file system is the
Enhanced Write Filter (EWF), which is delivered with the embedded versions of Windows
operating systems.
When EWF is enabled, the operating system stores the data of the file system in the main
memory during the booting process and thereby prevents writing directly to the data carrier.
As a result, only the data in the main memory is affected if the power supply is cut off. The file
system on the data carrier will not be damaged.
Although the EWF protects the entire partition, it also prevents the possibility of having data
persistently stored on it. Storage appears to occur, but then the data is only in the main memory
instead of in the memory device.
To have data written to the memory device, first the EWF has to be disabled and the system
has to be restarted. This means it is impossible to save data when a PLC is running unless the
desired protection for the file system is exited first. However, the non-variable components of
the CODESYS runtime environment (software, licenses, configurations) can be protected by the
EWF filter.
For this purpose, multiple partitions are set up on the MC6 motion controller. One of them
contains the operating system and the non-variable components of the CODESYS runtime
environment. This partition is protected by the EWF. Other partitions are released for writing and
can be used for storage of the boot project and, if necessary, of data created by the PLC
application.