Can I disconnect a USB drive while copying is paused in Windows 8?

As you all probably know by now, Windows 8 consolidates all simultaneous file copy operations into one single dialog. Also, wonder of wonders, you can now pause any of the operations as well!

New WIn8 Copy Dialog

What I want to know is, if you pause a file copy to/from an external drive, does Windows complain if you try to safely remove the drive? What about if you just disconnect the drive (when write caching's disabled of course) and then reconnect it to the same USB port and provided it has the same drive letter as before - does the copy continue normally and is the file copied properly?

I have Windows 8 only in a VM as of now (so that adds an extra USB Virtualization Connector Driver layer and who knows what else), plus for some reason none of my working USB sticks are at hand and I do not want to risk testing with my hard drives that contain my backups and other precious data. So is anyone with a proper non-VM non-VHD full Windows 8 RTM install willing to test this and let us know?

Also, I could not find any official word on whether this sort of operation is supported, or whether Microsoft clearly recommends no drive disconnection in such a scenario. If any official documentation can be found about this feature beyond what's there in this blog post, please do share.

Karan

Posted 2012-10-25T01:52:32.733

Reputation: 51 857

2I wouldn't unplug a drive, even if the copy is paused. This can corrupt the file system on the external drive. – None – 2012-10-25T02:25:04.647

@RandolphWest: Well I generally don't disconnect drives without safely removing either, even with write caching disabled, although it's supposed to be safe. But what I want to know is, with this new pause feature is it possible (and safe) to do so if the occasion demands it? Say I urgently need to use the USB stick on another PC but would not like to restart a massive copy operation all over again (not to mention that even cancelling wastes a lot of time). – Karan – 2012-10-25T02:32:21.527

@avirk seems to think it's possible. See that answer below. – None – 2012-10-25T02:33:40.690

1@RandolphWest: Copying occurs at a higher level than the file system, it doesn't corrupt the file system if the metadata is correctly flushed. But it would corrupt the file contents, yes. – user541686 – 2013-03-10T02:22:18.630

Answers

You can Safely Remove after pausing the USB data transfer so there is no chance of corrupting your device partition or your data.

enter image description here

Edit: Sorry I forgot to mention I disconnected the device and reconnected it and resumed the copy process without any problem.

Update: After starting the transfer I paused the copy process, ejected the USB drive, inserted another USB drive with different files, disconnected that drive as well, reconnected the first one again and finally restarted the copy process and it got resumed without any problem.

As you asked in the comments about how the data transfer might be affected if the drive letter is changed, in that case when you try to resume the process Windows prompts you that the source file is missing and displays the following three options:

Try again

Skip

Cancel

If you press the Try again button it restarts the process from the beginning.

I have only USB 2.0 ports so I can't tell you about any change when USB 3.0 ports are used.

avirk

Posted 2012-10-25T01:52:32.733

Reputation: 15 151

Ok, that's half-way there. Can you try the rest? That is, reconnect, resume the copy, and if successful, compare the MD5/SHA1 of the copy to the original on the source drive to determine that no corruption took place. – Karan – 2012-10-25T02:35:14.567

1@Karan - Try it yourself. – Ramhound – 2012-10-25T02:40:30.923

@Ramhound: Oh I definitely plan to, as soon as I have a proper RTM install to play with, and will add any useful results gleaned to my post. BTW, why the multiple comments saying the same thing? In any case, the question is not just about eliciting user experience, but also trying to figure out if there's any official word on this. – Karan – 2012-10-25T02:44:55.163

1@karan updated it. rest will update soon as I'll access the pc. – avirk – 2012-10-25T03:13:43.567

Awesome, thanks a lot for looking into this! Although I'm thinking of various scenarios to further test this in future (varying number of files, mix of different file sizes, test with both USB 2.0 and 3.0 ports/drives, change the drive letter to see errors thrown and so on), this is a great start and we at least know now that it is possible. – Karan – 2012-10-25T03:19:48.160

Might want to blur out the file name :) – Sorean – 2012-10-25T06:34:53.143

@Karan check updated answer :) – avirk – 2012-10-25T14:12:38.653

Fantastic; am accepting that as per your very helpful experiment and answer, the scenario is indeed possible and pause+disconnect+reconnect+resume can indeed be accomplished without data loss some (most?) of the time. Hopefully won't need to do this, but good to know it doesn't outright fail if ever the requirement is there. – Karan – 2012-10-25T18:27:12.560

It will not damage the drive, but at the same time, there is

No guarantee that you will be able to resume the copy
Assuming that you pause the copy file mid-file, that file might simply be as good as junk.

You will be able to remove the drive safely, but that's about all you can be guaranteed.

soandos

Posted 2012-10-25T01:52:32.733

Reputation: 22 744

So you're saying resumption may or may not be possible? I was hoping for some repeated testing to actually confirm what really happens, since I could not find any official word on this. – Karan – 2012-10-25T02:37:26.217

I would expect that it would probably work if no new drive gets plugged into the computer in between and the drive is not written to in the interim. I would not expect any guarantees. – soandos – 2012-10-25T02:38:39.790

@Karan - So test it? – Ramhound – 2012-10-25T02:40:00.067

I suspect you won't get any official word that says "yes, it's ok to do this" because even if the system is designed to deal as gracefully as possible with this scenario, it's still got potential to invite problems and Microsoft aren't going to create support issues for themselves needlessly.

For instance, what if you unplug your drive from one USB port and plug it back into another - what should happen then (I know you talk about the same port in your question, but in real world use, how likely is that to always happen)? What if you unplug the drive, plug it in somewhere else then return to the original computer? Again, something that could well happen in the real world that has to be anticipated.

Rob Moir

Posted 2012-10-25T01:52:32.733

Reputation: 647

I would suppose (I plan to confirm later) that a change of port but keeping the same drive letter would not cause any problems. As for using the drive in the interim on another PC, that's precisely the scenario I had envisaged (see my comment to Randolph above). Again, I would hope that as long as the partial files are not touched, the process can be resumed. I also want to know/check whether the partial files have some sort of special extension appended, or ADS if on NTFS etc. to indicate that the copy process is not yet complete. – Karan – 2012-10-25T08:43:49.100

As far as official docs go, I suppose you are right, but I don't see any problem with them mentioning (even if it's an informal blog post by an employee) that they tested this scenario and found it to work, but it's not guaranteed so users can't complain if it fails. – Karan – 2012-10-25T08:44:48.647

Crikey! Why would you want to?

I wouldn't trust this even if Microsoft said it was supported. I value the integrity of my data far too much to risk it over something as trivial as a little convenience.

Instead I would split my copy jobs up into manageable chunks- and copy them separately (instead of pausing). But that's if I wanted to do it using Explorer- and I wouldn't.

You are better off learning how to use Robocopy (built into Windows 8) instead of Explorer for much larger file copy/move jobs anyway. It's faster, more customizable, maintains file timestamps, and doesn't get stuck if a file is locked and abandon the copy job......

......... and you CAN effectively pause it. If you interrupt a Robocopy job (control + C in Command Prompt), then run it again after reconnecting your drive again, it rapidly skips all the files that already exist in the destination and starts copying where it left off.

Austin ''Danger'' Powers

Posted 2012-10-25T01:52:32.733

Reputation: 5 992