Data saved in flash (FDS) that were previously retained are erased during DFU on some devices

[clockis]

Hi All,

In our product we have noticed that, on a few occasions, some important information that is saved using FDS (in a file with ID: 0x02) are being erased when an OTA update is performed. On most occasions these data are retained after an OTA update but on some occasions they are not retained. 

This has happened when updating with the same application versions on different occasions(seeing different results, in one occasion the data are preserved after the DFU in others they are not after the DFU) and the bootloader was never changed in years.

What could be causing this?

Thank you very much for your time. Any feedback is appreciated.

Best regards

[Hung Bui]

Hi Stavros, 

We would need to look into how you configured the bootloader to preserve data of the application when doing DFU (NRF_DFU_APP_DATA_AREA_SIZE). 

By default this space should match with the number of pages used by FDS/fstorage (include the gabage collection page) 

Please be note that even though the file ID is not change, the location of the file is not fixed to one single page. There is a chance that the issue happens when the file is located at the last page and it might be erased if the configuration for reserved page is not correct.