How to debug hard drive power saving?

My harddrives are not going to powersave.

I have added the following lines into /etc/hdparm.conf:

command_line {
    hdparm -S 25 /dev/disk/by-uuid/42d40d37-2859-457c-93d0-e4c617d06d9f
}

command_line {
    hdparm -S 25 /dev/disk/by-uuid/e7274b44-09e1-4a3c-90e7-01327f8ed8d4
}

command_line {
    hdparm -S 25 /dev/disk/by-uuid/71223a72-6e5b-4075-9170-1e5f0217798c
}

but they apparently have no effect.

$ sudo hdparm -C /dev/sdc

/dev/sdc:
 drive state is:  active/idle

all the time.

How to know if it is configuration problem or some disk activity wakens the drive? If it is disk activity, then how to know if it is it and which it was?

My OS is Ubuntu 14.04.1 LTS.