Matrix Vision mvBlueLYNX-X, Техническое руководство, Страница: 94 / 236

11.6 Storing Data On µSD Cards or USB Devices
Write cycles of Flash memories like SD card or memory sticks are limited. To extend the life cycle of
the internal µSD card, we suggest not to use it for logging. For logs, please use a mounted network
directory, a USB stick or an external µSD card.
You can easily damage the µSD card or the mechanics of the mvBlueLYNX-X by improper operation.
Please be careful when inserting, removing, or handling the µSD card. Keep the µSD card at right
angles to the backplate when inserting it into the slot!
11.6.1 Powering Down The Camera
The mvBlueLYNX-X is a small computer with a file system stored on µSD card. Just like desktop PCs it
usually makes sense to power down the camera in a controlled manner instead of removing power suddenly.
The journaling file system used for the internal µSD card is designed to ensure that the file system is not
permanently damaged by a power outage but the individual files being written at the time may not be
complete. If you are certain that data is not being written to the internal µSD card and that all previously
written data is already stored on the card (see below for a method to confirm this), then removing power from
the camera in an uncontrolled manner is permitted.
11.6.2 Precautions
The following precautions may be useful to preserve data integrity if applications do write data to a µSD card:
Wherever possible make use of the standard GNU/Linux commands
halt
,
reboot
or
shutdown
instead of suddenly removing power from the camera.
1.
After installing software or updating the camera with the
opkg
command or writing any data to a
µSD card or USB memory device always use the
sync
comand before removing power.
2.
In user applications that must write data to a µSD card or to a USB memory device ensure that a
sync
function call is made to flush all write buffers to the card before removing power to the camera.
3.
Avoid writing data to the internal SD card. If this is not possible then ensure that the write buffers are
not written to the card more than is absolutely necessary. e.g. if you write log messages every second
but flush the buffers (with
sync
) only every 30 seconds, you may improve the lifetime of the µSD
card at the cost of losing up to 30 seconds of data due to a power outage. Depending on your
application this may be an acceptable compromise.
4.
Consider using an external USB memory device or a µSD card in the external SD-slot or a network
directory for application data or logs. In this way the camera's system files will not be affected by a
power outage or data loss on the storage device used. 5.
For data that does not need to be preserved after a power outage or camera restart consider using a
RAM disk to store data e.g. use the
/tmp
directory.
6.
mvBlueLYNX-X Technical Manual
84 22 April 2016 Version - 1.49 MATRIX VISION GmbH