Further investigation:
For testing I’ve changed the spindown idle time to 5 seconds.
hdparm -S 1 /dev/sda1
/dev/sda1:
setting standby to 1 (5 seconds)
And yes, the drive spins down. But unfortunately it starts to spin up right after the spindown. And 5 seconds later it does the same thing all over again.
Setting the spindown idle time back to 15 minutes:
hdparm -S 180 /dev/sda1
/dev/sda1:
setting standby to 180 (15 minutes)
And the drive keeps spinning.
lsof says that there are no processes running on the mountpoint (/mnt/data) or the disk (/dev/sda1).
I also followed these steps to ensure that nothing is running, that could access the drive.
http://info4admins.com/tips-to-spindown-your-hard-disk-in-debian-or-ubuntu/
I’m getting more and more the idea that there is some kernel process interfering.
Is anybody else experiencing the same issue?
Thx.