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The green led (ACT) on my Raspberry Pi 3 is set to mmc0 to flash on SD card activity via

echo mmc0 |sudo tee /sys/class/leds/led0/trigger

However, it flashes much more often (randomly every few seconds) than it should according to 

iotop -bktoqqq -d .5

and

iostat -dzp 5

So I wonder what is the light indicating if nothing is read or written to the SD card for many seconds or minutes.

Has anybody seen this LED off for longer periods in the mmc0 mode or does it always flash unrelated to SD card I/O on a Raspberry Pi 3?

It also has an mmc1 mode, in which it flashes even more frequently. I wonder what that indicates.

Why does it matter? After a colleague pointed out that Raspberries kill SD cards, I wanted to reduce my writes to my SD card in order to increase its lifetime and was expecting a less flashing LED indicating some sort of success. Now I am worried that the controller is still messing with it.

flakeshake
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1 Answers1

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I have also asked this question Why is the green LED (ACT) blinking without SD card activity also at the Raspberry Pi Forum and received this answer:

by rpdom ยป Wed Feb 22, 2017 8:02 pm

From what I understand, the Pi sends a "status" request to the card every few seconds to check that it is still there and working. That will cause the LED to flash, but won't cause any data to be read or written to the card itself, just the controller on the card. It won't cause wear.

I have not had a Raspberry kill an SD card yet, and I have several of them, some of which have been running for a few years.

But also questions about the mmc1 mode and documentation remain.

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