How to spin down hard disc in KDE

[Inkit]

I have LMDE installed on my system, pointing to the latest repos. I have moved over to using xfce and KDE (I installed the KDE-full package from the repos) after up4. In xfce, I've got the power manager setting set so that my desktop goes to sleep mode after 30 min of inactivity. I've got the same basic setting in KDE too.
I have two internal HD's with only one OS installed in sda. I have everything I need on this drive and only use sdb as a backup for my data. This backup is taken a couple of times a week. At other times, this drive is basically unused.
When on xfce, I notice that sdb spins down after half an hour. I know this happens because when I mount sdb to take a backup, and if my comp has been running for more than half an hour, I can hear the disc spin up when I mount it.
This however does not happen when on KDE, and the disc is spinning throughout. I was wondering if there was some way to make sdb spin down after a certain amount of time? I've hunted around and found hdparm. Unfortunately everything on this file is commented out. Also I don't know how to set the spin down times only for sdb and not for sda.
Can anyone help me with what I have to do to get hdparm to spin down only sdb after say 30 min. I would also appreciate anyone letting me know of any other tool that can accomplish the same purpose.

[äxl]

couple of times a week

Best: Plug them in only if you need them. If you need need them daily: Just leave it on. Wear-off is worse than 3-10 Watts per HDD I guess ...

Cause I don't know if hdparm with UUID is possible ...?

[Inkit]

Sorry for the delayed response axl but I was traveling and didn't have access to my comp. As for your suggestion, I was coming round to thinking the same anyway, so I guess there's nothing much I can do. As you say, spinup and spindown probably cause more wear than if they keep spinning.