Technical data • Individual components
Chapter 2
Technical data
Panel PC 2100 swing arm user's manual V1.00
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3.3 CFast cards
3.3.1 General information
CFast cards are storage media that are easy to exchange. Due to their robustness against environmental influences
(e.g. temperature, shock, vibration, etc.), CFast cards are ideal for use as storage media in industrial environments.
CFast cards are a development derived from CompactFlash cards that use the SATA protocol instead. CFast cards
are not compatible with CompactFlash cards.
3.3.2 Basic information
In order to be suited for use in industrial automation, CFast cards must be highly reliable. The following items are
very important to achieving the necessary level of reliability:
•
The flash technology used
•
An efficient algorithm for maximizing service life
•
Good mechanisms for detecting and fixing errors in the flash memory
3.3.2.1 Flash technology
CFast cards are currently available with MLC (multi-level cell) and SLC (single-level cell) flash blocks.
In addition to a service life that is 10 times longer than MLC flash components, SLC flash components also have
write/delete cycles that are 33 times faster, making CFast cards with SLC flash components the preferred choice
for industrial environments. These factors are still heavily dependent on the actual application, however, so that
no blanket statement can be made.
Due to increasing cost pressure as well as improved wear level algorithms and monitoring features (S.M.A.R.T.),
MLC flash technology is still widely used in this market.
3.3.2.2 Wear leveling
Wear leveling is an algorithm that can be used to maximize the service life of a CFast card. There are three different
algorithms:
•
Dynamic wear leveling
•
Static wear leveling
The basic idea behind wear leveling is to distribute data over a broad area of blocks or cells on the disk so that
the same areas aren't deleted and rewritten over and over again.
3.3.2.2.1 Dynamic wear leveling
Dynamic wear leveling makes it possible to utilize unused flash blocks when writing to a file.
If the disk is 80% full with files, then only 20% can be used for wear leveling.
The service life of the CFast card is therefore dependent on the amount of unused flash blocks.
3.3.2.2.2 Static wear leveling
Static wear leveling monitors which data is rarely modified. From time to time, the controller then moves this data
to blocks that have already been used frequently in order to prevent further wear on those cells.
3.3.2.3 ECC error correction
Bit errors can be caused by inactivity or when a certain cell is being operated. Error correction coding (ECC)
implemented via hardware or software can detect and correct many errors of this type.
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 important parameters and quickly detect imminent failures. Critical performance
and calibration data is monitored and stored in order to help predict the probability of errors.
3.3.2.5 Calculating the expected service life for an existing application
The following procedure can be used to better verify whether a CFast card with SLC or MLC technology should
be used in a particular application.
