Is it safe to power off disk after hdparm spin-down? I have heard that it is generally considered unsafe to power off a mounted hard disk; the consequences could be a lost or unresponsive drive. However, powering off a drive after unmounting should be no problem. I am using hdparm to spin down my disk automatically after two minutes of inactivity. The drive spins down but is still mounted - and accessible, too. If, for instance, I issue the command `ls /media/external/drive/` the shell hangs for a few seconds until the disk is up and running again. My question is: Is it safe or unsafe to power off a drive in a "mounted" AND "spun-down" state?

It is safe if you also ensure it won't spin up in the process, i.e. nothing will access the device. You'd better ask the kernel to forget about it before unplugging, in case of Linux: `echo 1 > /sys/class/block/sda/device/delete`.