Who wakes up the hard drive?
 

How to find out which application wakes up a hard drive?

"hdparm -C /dev/hdb" shows that it's "standby".
Then, after some time, I check it again, and now it's "active/idle".

A long shot, but may be you can use 'lsof' ?

"lsof" does not seem to help.

What if some process queried something from the disk, and either this query closed the file immediately after opening, or was not associated with a file at all?

I guess I need something that would monitor/log any access to the hard drive to some file...

I unmounted this drive, and this behavior still reproduces.
So it must be some process that works with devices directly that wakes up the hard drive.

Any ideas?

Your help will be greatly appreciated!