JerPa - I believe your fears are accurate…that the fan NEVER really turns on. There seems to be some bug, I think now too after testing mine, thanks in large part to the commands you cited.
Here’s what I did first. I have only one hard drive in my EX2 (I run in JBOD) and two USB hard drives connected. I know both the internal and one of the two USB drives, which is a WD drive, always goes into sleep mode after 10 mins, but the other USB drive, a Hitachi one, never falls asleep and so there is always a noise from that drive constantly spinning. So I ran a command to force sleep all 3 (just to be sure)…which is hdparm -y (i.e. hdparm -y /dev/sda, hdparm -y /dev/sdb and hdparm /dev/sdc). After I issue these commands all go into forced sleep (they wake up when you access them).
But before I put them to sleep, I ran ‘fan_control -g 0’ and ‘temperature_monitor -b’ and ‘temperature monitor -c 0’ (since I have just one internal drive. And yes, running them validated your point that the Current temp from fan control is indeed the board temp. So I got the value 53C for board temp and 41C for my sole hard drive.
After getting these readings, I then put the drives to sleep, and the noise from around the EX2 came to immediate halt - not the slightest sound of a fan running. Then I took a second reading (with the drives shut asleep) of the teps and I got the same values again - including 53C for board.
So…I know that in the system_init script (the initialization script that runs when EX2 is turned on), the fan control is run based on the /etc/fan_temperature.txt file. And according to that file, whose contents I already cited, the fan’s start/stop threshold is 39C. Regardless of whether that is the board temp or the hard drive temp, I was getting readings higher than 39C for both but still the fan was not running. Which does seem to confirm your thoughts…that the fan never comes on automatically even when it breaches WD’s threshold.
The thing is though, IF we want WD to formally take this up as an issue, we cannot just discuss it here. Someone needs to either submit a support request or call support and have them open a support request. I am not feeling like it Will someone else please do the honors - and then point them to this post and the previous post by JerPa. There’s enough material evidence in these two posts to make a case that the fan seems to be just for cosmetic purposes only…it never seems to get triggered. If you, JerPa, wish to open the support case…or someone else willing to volunteer, that’ll be great.