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I have a netbook connected to two USB HDDs when I'm at home, and most of the time when I take it with me I shut it down and then disconnect it. But sometimes (mostly monday mornings ;) ) if I'm in a hurry, I may just tell it to sleep and then disconnect everything. Is this safe? Does Windows 7 eject the drives or write the buffers to disk so that there's no risk of data corruption, or do I need to do the "safely remove hardware" routine before putting the PC to sleep?

Running Windows 7 Home Premium x32. Note that the drives are for data storage and no apps are running from them.

EDIT: I've noticed that my drive powers down before the computer goes into sleep mode. This seems to suggest that Windows automatically performs the same actions before dropping to a lower power state as it does when I safely remove the USB HDD.

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up vote 2 down vote accepted

While it is probably best to use 'safe remove'....
Removing usb while in the sleep mode will not damage anything.
With most USB devices, you should be able to remove/add them in suspend without encountering any issues. When it wakes from sleep it expects the hardware to be there but generally it will carry on - it should have no effect on the usb but is a computer OS side reaction.
This appears to be also true with an encrypted usb (it also goes into this in the answer).
See all Gray areas.

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I think as long the usb drive is not accessed, its safe to unplug it, so if your computer finish the sleep mode, its safe.

So far never had a data corrupt drive as long I close all the explorer and applications that opening/writing a file in it

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I've had one Buffalo drive crap out on me because of hibernation, so I'm a bit cautious and would like to know a definite answer... – onik Nov 4 '11 at 6:45
@onik: depending on how this "drive" crapped out on you, we can't even be definite it was due to Windows. When the power state is changed, Windows does its thing. Each program and device driver is responsible for cleaning up its actions. So there possibly is a window of corruption, but there are so many links in the chain, it is really hard to blame any one link. On top of that, each motherboard manufacturer can implement the sleep states slightly differently. – surfasb Nov 4 '11 at 8:32
@surfasb The HDD did a partial entry into the Master File Table, and didn't complete it after waking up, which resulted in a corrupt MFT. This was mainly due to a bug in the firmware of the drive, which emphasizes your point about multiple variables affecting the safety. – onik Nov 4 '11 at 12:35

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