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This component is used to store data that persists across device reboots, e.g. the latest state of a light or the accumulated energy used by an appliance. The data is normally stored in flash memory; the host platform stores it in a file instead, and on ESP32 it can optionally be kept in RTC memory.

# Example configuration entry
preferences:
  flash_write_interval: 1min

Configuration variables

Section titled “Configuration variables”

  • flash_write_interval (Optional, Time): Customize the frequency in which data is flushed to the flash. This setting helps to prevent rapid changes to a component from being quickly written to the flash and wearing it out. Defaults to 1min. Set to never to disable this feature.

  • rtc_storage (Optional, boolean): Only useful on ESP32. Compile RTC-memory-backed preference storage into the firmware even when no other option selects it (options such as safe_mode’s and fast_connect’s storage: rtc enable it automatically). This is intended for external components that request RTC storage through the C++ preferences API; without it, such requests fall back to flash (NVS) with a warning in the log. Not available on ESP32 variants without RTC memory (C2 and C61). On ESP8266, RTC storage is integral and always enabled: true is accepted (and does nothing), while false is rejected since it cannot be disabled.

Flash Wear

Section titled “Flash Wear”

As flash memory has a limited number of write cycles, flash_write_interval reduces the number of flash writes caused by rapidly changing components. In the past, when components such as light, switch, fan and globals were changed, the state was immediately committed to flash. This meant those components always restored their most recent state after power loss, but at the cost of potentially damaging the flash when they changed frequently.

To mitigate this, the state is now first stored in memory and only flushed to flash once the flash_write_interval has passed. This results in fewer flash writes, preserving the flash health.

This behavior can be modified by setting flash_write_interval to 0s to commit the changes to flash as soon as possible. Be aware that this may lead to increased flash wearing and a shortened device lifespan!

For ESP8266, restore_from_flash must also be set to true for states to be written to flash.

See Also

Section titled “See Also”