Hi,
I recently purchased a new 1TB seagate harddisk to store backups of my music, movies etc. I use paid software in Windows 7 to manage backups. However I run the software once every month and so the hard disk gets used only then. Rest of the time it just remains idle. And I use linux most of the time and the secondary hard disk is never mounted on linux. So I just wanted to know if there was a way to shutdown the second hard disk using linux. I dont want it spinning uselessly when I am using linux.

I presume your talking about an internal hard disk? If so, I don't know of any way in Linux to power down a secondary internal hard disk.

As soon as you turn on your computer, power is already going to the internal disk whether it's mounted or not so long as a power cable is connected to it. Unless your secondary hard drive is inefficient and consumes a lot watts, the amount of power it draws at idle is very negligible.

You could always just open your computer case and unplug the disk's power connector when not in use, just make sure the whole computer is powered off and the AC cord is unplugged so you don't shock yourself.

You can shutdown that disk with hdparm. Have a look at the -S option.

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Thanks for that, I learned something.

Unless you are running odd BIOS settings, the HDD spins down after 'X' amount of time (normally about 30 minutes IIRC). Setting the spin-down time in the BIOS isnt hard, its normally under 'power management'.

I know that but I don't want to disconnect and connect it every week I run backups.

Can you please tell me how to set the spin down time on hdparm? I want to set the time to 10 mins. The encoding of timeout value is odd and I couldn't figure out anything after reading the man pages.

Try (as root) hdparm -S 1 /dev/sdb (or whatever the disk is labelled as)
The disk should spin down after 5s and remain like that until it is next accessed.

For 10 minutes you need a value of 120.

Is this change permanent or do I have to run this command after every boot?

You will have to do that after every boot. If you want the command to be run automatically just add it to your rc.local-file.

Isn't there some file which I can edit to make this change permanent? BTW do I need to add sudo before the command when I place in rc.local?

You can't make that permanent, the drive resets when you boot/reboot the machine.
All commands in rc.local run as root, so you don't need sudo.