I posted this before in "Newbie", but I got good answer. Maybe here anyone can give the very hint.

My problem is the following: I have two harddisks,

hda = Linux
hdb = Windows

When running Linux (as I usually do since about 7 years), either my BIOS should stop hdb after four minutes, or I force it to spin down with

hdparm -y /dev/hdb

Note that the harddisk is not mounted!
After a few seconds, about 10 seconds, hdb spins up again. This happens in my Mandrake 10.1.

Furhter notes:
* When using my Debian Live, the disks stops and keeps stopped.
* Even in Mandrake 10.1 (never updated in any way) this worked for about 1 and a half year.

Has anyone any good suggestions what the reason for the hdb to spin up could be?

Perhaps it could be the auto-mounter, 'seeing' the hard drive out there, and trying to spin it up and get it ready. Haven't used Mandriva/Mandrake in a couple of years, though.

Just a guess.

This is, what mount says (after hdb spinning up), so there is obviously nothing about an automounter:

/dev/hda1 on / type ext3 (rw)
none on /proc type proc (rw)
none on /proc/bus/usb type usbfs (rw)
none on /sys type sysfs (rw)
/dev/hda6 on /home type ext3 (rw)
none on /mnt/cdrom type supermount (rw,noexec,nosuid,nodev,sync,users,dev=/dev/hdd,fs=iso9660,--,umask=0,iocharset=iso8859-15,codepage=850)
none on /mnt/floppy type supermount (rw,sync,dev=/dev/fd0,fs=ext2:vfat,--,umask=0,iocharset=iso8859-15,codepage=850)
none on /mnt/ramfs type tmpfs (rw)

Hard drives life spans gets worst when they have to spin down and then up. I suggest keeping them on or before turning on the computer just disconnect power from the unused hard drive. If you want to save power, I suggest putting the drive in sleep mode after 24 hours have lapse. If you are not going to use the drive after 24 hours, there is a good chance you will not be using it.

Controllers and hard drives can wake up other hard drives if they are in sleep or stand-by mode.

supermount is Mandrake's or Mandriva's automount which I hate. hal, dbus and maybe udev are better for automounting.

Thank you, Electro, these are the first good thoughts, but they have some problems:

I never let my computer simply turned on, so 24 hourse are exeggerated. Usually I can say that I'm not using hdb in Linux any way.

Supermount is not a Mandrake/Mandriva-sickness. You can turn it on or off any time you want by modifying /etc/fstab in any Linux.

Disconnecting the power cord was also already a though of mine, but I realised, that my mainboard reacts strange on it and does not bring up the system in any way then.

Still I wonder why it HAD WORKED the same way I do for a long long time.

Okay, I could point out the problem. It's not a Linux related problem. It's interesting that this (and other) problem(s) no longer occur when I use another power supply. There is definately a defect in the hardware of the power supply.