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  1. lbonillayanez
  2. PLCnext Technology & PLCnext Controls
  3. Tuesday, 11 May 2021
Dear colleagues, I have a client who asks me the following question:
- He needs to know how much is the maximum capacity that can be given to the sqlite datalogger, for example if an 8Gb SD memory is used in the PLCNext these 8Gb can be fully used for data storage? How do you advise me to size the memory if I need to store 3 real type variables?
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Oliver PLCnext Team Accepted Answer Pending Moderation
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Hello,
depending on how you use the SD card you can use the full card
or the Overlay will be placed on the card. ~50MB will be occupied by System Files in that case.

Usually there are more requirements on a Datalogger then the amount of variables.

How long is the period of time you want to keep in the log? - 1h? 1 Day? 1 Week? 1 Month?
How often do you want to store the variables. 1ms 100 ms 1s 1min 10 min
Do you wish to create backups of the DB? -> use rollover mechanism , and copy finished DB files.
Do you have the possibility of powerloss -> better split up the DB into smaler chunks. In case of malformation smaller amounts of Data will be lost.

MaxDBFileSize / DataStoredPerCyle * Cyletime = TimeUntilFileSizeHasBeenReached.
DataStoredPerCycle= 3 * (Datatype + Datebytes + Status Bytes.)
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