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    Thanks. After umount an external hdd, is it safe to remove the external hdd from the computer? Commented Mar 4, 2015 at 21:05
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    I don't think umount is equivalent to "safely remove", and neither is udisksctl power-off, please see my comment on the other answer. Compare with the behaviour in Windows for example. My guess is that Windows does a bit more than just 'unmount' the filesystems on the device. I have observed it spinning down external hard drives, turning off LEDs on card readers (without subsequently rendering the device unusable unless replugged or the system rebooted), etc. Commented Jan 16, 2016 at 9:15
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    @ack - what does Windows have to do with this? and why are you guessing? and you do not have to reboot for it to become usable again. you umount it. then you power it off. and i never suggested anything regarding udiskctl one way or the other. Commented Jan 20, 2016 at 23:04
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    @mikeserv "Safely remove hardware" is the expression used in Windows. It is likely that other systems copied that phrase because of user familiarity. It is important to distinguish it from mere filesystem unmounting. An example of where this matters greatly is when the OS is uncertain about a storage device's write caching. I've personally experienced quite significant data loss (corrupted superblock and files) after merely unmounting and unplugging an external hard disk. I later found out that Linux had warned about this: "No Caching mode page found", "Assuming drive cache: write through". Commented Jan 22, 2016 at 15:57
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    @ack - no, that's not important. your problem is probably your acpi. it doesn't have anything to do with operating system exactly - just that your board manufacturer only wrote drivers for one os. those little multicard devices require fairly low-level access to the card target - they have to be able to do stuff like eye-fi. they're not block devices - they're character devices. they're nothing at all like usb disks. the board-rom has to handle them separately, and if your vendor poorly supports it (its not unusual - try booting from one) youre out of luck. but its not linux's problem. Commented Jan 22, 2016 at 16:44