chuck: Thanks for response, but it must be something else (I power off SD card with 300ms delay after calling file.close()) and problem is even with file.close() itself - it returns false - so, card initialization returns true, file.exist() returns true, file.open() returns true and file.close() fails - in this step is data written to card, am I right?
Another strange behavior is that, when I unplug card and put it back (while power is down), then everything works again... until another +/- 15000 cycles - how the card can recognize that it was unpluged, when there was no power? Or is there any posibility, that it is ATmega328, who is senstive to unpluging card? Like if it clears some data from RAM when program is running without card? (I don't use EEPROM)... RAM is volatile - should be erased after reset, or not?
I use SdFat 2015 03 24 and arduino pro 3V3/8MHz core for atmega328. On SPI bus is NRF24L01... but it has same behavior without it. I also tried short-circuit power imidietly after turn power off (if slowly falling supply voltage doesn't matters), but without any difference.
I'm attaching source code for ATmega328, there is writing to EEPROM for debugging, no difference without it.