> Are you running udisks?  If so then that is the culprit.  It polls the
 > drive's SMART stats every 10 minutes unless the drive is already
 > asleep, so if the timeout is>= 10 minutes ( which it seems WD drives
 > refuse to go any lower anyhow ), then the drive will never go to
 > standby.  I posted some patches to fix this a while back on the
 > devkit-devel mailing list but I think the udisks maintainer has still
 > not gotten around to applying them.

This is indeed the cause in my case. There are the two problems that
overlap: if a shorter time then 10 minutes is set as a standby time,
the WD disk rounds this up to 10 minutes.
And Kubuntu is using udisksd. It is started during a KDE login and
never stopped when logging out.

Is it possible to configure udisks to not do any polling or at a much
longer interval? Or is it possible to safely disable udisksd somehow?
I'm still looking for a practical solution.

regards
Patrick