Technical data
54
Automation PC 3100 User's manual V 1.00
Translation of the original documentation
2.3.3 CFast cards
2.3.3.1 General information
CFast cards are easily replaceable storage media. Due to their robustness against and environmental influences
(temperature, shock, vibration, etc.), CFast cards offer optimal values for use as storage media in industrial envi-
ronments.
CFast cards are a further development of CompactFlash cards, but the SATA protocol is used here. CFast cards
are not compatible with CompactFlash cards.
2.3.3.2 Basic information
CFast cards used in industrial automation must be extremely reliable. To achieve this, the following points are very
important:
•
The flash technology used
•
An efficient algorithm to maximize service life
•
Good mechanisms for detecting and correcting flash memory errors
2.3.3.2.1 Flash technology
CFast cards are currently available with multi-level cell (MLC) and single-level cell (SLC) flash blocks.
SLC flash devices have a service life 10 times longer than MLC flash devices and are characterized above all by
33 times the number of write/erase cycles, which makes CFast cards with SLC flash blocks the preferred choice
for industrial applications. These factors are strongly dependent on the application, however, so that no general
statement is possible.
Due to increasing cost pressure, improved wear level algorithms and improved monitoring features (S.M.A.R.T.),
MLC flash technology is increasingly finding its way into this market.
2.3.3.2.2 Wear leveling
Wear leveling refers to an algorithm that can be used to maximize the service life of a CFast card. A distinction
is made between the following algorithms:
•
Dynamic wear leveling
•
Static wear leveling
The basic idea of wear leveling is that data is distributed over a wide range of blocks or cells on the data storage
medium so that the same areas do not always have to be erased and reprogrammed.
2.3.3.2.2.1 Dynamic wear leveling
Dynamic wear leveling offers the possibility to use unused flash blocks when writing to a file.
If the data storage medium is already 80% full of files, only 20% can be used for wear leveling.
The service life of the CFast card therefore depends on the unused flash blocks.
2.3.3.2.2.2 Static wear leveling
Static wear leveling additionally monitors which data is rarely modified. From time to time, the controller moves this
data to blocks that have already been programmed frequently to avoid further wear and tear of the cells.
2.3.3.2.3 ECC error correction
Inactivity or operation of a particular cell can cause bit errors. Error-correcting code (ECC) implemented by the
hardware or software allows many such errors to be detected and corrected.
2.3.3.2.4 S.M.A.R.T. support
Self-Monitoring, Analysis and Reporting Technology (S.M.A.R.T.) is an industry standard for mass storage devices
that has been introduced to monitor key parameters and detect imminent failures at an early stage. Monitoring and
storing critical performance and calibration data attempts to predict the probability of error states.
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