Which process wakes-up USB-drive?

Try these suggestions:

- see if there are any cron jobs with a 30 minute repeat rate. If there are any, they'll be in one of the /etc/cron.* directories

- run "systemctl", which uses less to display a list of all systemd services, showing which are loaded and active together with a short description of what the job does.

- run 'top' in a terminal window and watch it as the time for the disk activity approaches.

- Better, run

ls -s /var/log/*

Make a note of all the logs with a timestamp thats a bit *later* than the last time you know the disk was woken up, and use 'less' to see what, activity was logged at that time. Then scan through these logs to see what happened at that time. There probably won't be more than half a dozen logs to look at.

Hint: if you look for the last ocurrence it will be near the end of the log. Be sure to use a command like: sudo less /var/log/syslog

to look at the log: log files are only intended to be read by the sysadmin, which is why you need to prefix the command with 'sudo' and provide a password when asked.

If you've never used 'less' before, do read its manpage because its got very powerful file searching abilities, all triggered with with single key commands. Its one of the essential Linux tools that you really should know how to use.

I'd also try: sudo lsof | grep /media where /media is (part of) the path to the USB-HD.

It's trickier if your root fs is on the HDD, because everything will be living there.

For processes you might also run:

ps axl | awk '$10 ~ /D/'

which will tell you everything that's waiting on I/O. You could log that in a file:

#!/bin/sh while true; do ps axl | awk '$10 ~ /D/' >> unintsleep.log done

(although that may cause a feedback loop if the logging causes its own I/O to block)

Theo

Thanks for the advice. We had a power outage last night. Since then the external drive sleeps as it should. Therefore: no chance to identify the root cause.

Bye, Stefan (semi-happy with the current state)

Keep watching it. Remember the old saying "Problems that go away by themselves come back by themselves".

It may be a sequence of events that causes the problem, and that sequence may take a while to happen.