I am running Kubuntu from External Hard Drive. My Internal Hard Drive has Windows on it. I don't want to use it while on Ubuntu and want to turn it off to produce less heat as well consume lower battery. I think spinning down hard drive isn't an option for me. Because, it wear out the hard drive and I don't plan to spend on HDD's :)
sudo hdparm -Y /dev/sdX
where /dev/sdX is the device you'd like to turn off. You can also run
sudo blkid to determine the device's 'fingerprint' (UUID), which would allow you to more reliably control which device is being turned off.
In this case, you'd run:
sudo hdparm -Y /dev/disk/by-uuid/DEVICE-IDENT-HERE
-Y Force an IDE drive to immediately enter the lowest power consumption sleep mode, causing it to shut down completely. A hard or soft reset is required before the drive can be accessed again (the Linux IDE driver will automatically handle issuing a reset if/when needed). The current power mode status can be checked using the -C option.
You likely have the
udisks2 package installed; you can use
udisksctl power-off -b /dev/sdX
/dev/sdX is the device you'd like to turn off.
udisksctl man page (version 2.7.6):
power-off Arranges for the drive to be safely removed and powered off. On the OS side this includes ensuring that no process is using the drive, then requesting that in-flight buffers and caches are committed to stable storage. The exact steps for powering off the drive depends on the drive itself and the interconnect used. For drives connected through USB, the effect is that the USB device will be deconfigured followed by disabling the upstream hub port it is connected to. Note that as some physical devices contain multiple drives (for example 4-in-1 flash card reader USB devices) powering off one drive may affect other drives. As such there are not a lot of guarantees associated with performing this action. Usually the effect is that the drive disappears as if it was unplugged.