I have a Raspberry Pi3 Model B+ that is used as a backup server.

The backup tool is configured to write all data to an external NTFS formatted drive. However, the SD card is constantly accessed (written on and/or read from) as indicated by the flashing green LED (irregular pattern).

How can I find out, which process is causing this?

I tried using iostat, however that only confirms that the SD card is constantly in use:

  tps    kB_read/s    kB_wrtn/s    kB_read    kB_wrtn Device
 7.59       493.9k        27.0k      41.1G       2.2G mmcblk0
28.16       695.5k         1.4M      57.9G     118.9G sda

(kB_read and kB_wrtn are accumulated values over ~24 hours)

Another tool that I tried is iotop, but this gives me only information on all processing that are causing IO traffic, but it cannot distinguish between SD card and external NTFS formatted drive. Processes listed here include:

  • urbackup (the backup tool, configured to use the external drive as a tmp directory and backup target, backup sources are other PCs on the LAN)
  • some kworker/u8:0+flush-8:0 or similar processes which I don't know about
  • mount.ntfs-3g

As the SD card is constantly accessed I am worried about it beeing destroyed in the near future.

Any ideas what is causing this or how can find this out?

2 Answers 2


I've had a lot of success with the output of lsof which has data correlating a PID with the file that's being opened. That's how I ended up figuring out that my flash drive kept blinking whenever I looked at it because I had accidentally set motion up to start on boot up. It was quite a creepy effect!


The SD card is accessed twice a second to check that it is still inserted.

This results in a very brief LED flash twice a second which most people don't even seem to notice.

  • 1
    In my case, this is note the case. The green LED is flashing in an irregular pattern and iostat confirms that a lot of data is written/read. I just updated my question with the actual output of iostat. Nov 24, 2019 at 21:08
  • @user1251007 That's fine now,
    – joan
    Nov 24, 2019 at 22:32

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