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External Hard Drive Not Copying Data

I’m attempting to copy data from an external hard drive to an internal one on my new (to me) 2012 Mac Pro, 10.13.6. The data begins to copy but the progress bar is stuck at 26.6 mb out of the 900gb data. I’ve attempted to cancel the transfer before, but it ends up freezing and I have to hard reboot my machine and it disconnects my external HD, causing issues with that. The internal hard drive I’m trying to transfer to is a toshiba dt01aca100 and my external HD is a WD My Passport 25E2. Thanks for any help.

Mac Pro

Posted on Sep 16, 2020 11:06 AM

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Posted on Sep 16, 2020 12:18 PM

If you are seeing elongated copy times, it suggests the source drive may have many Bad Blocks.


If the source drive is developing Bad Blocks, the standard resolution is to reread the data block, continuing to run the raw data through to drive's error-correction circuits, in hopes of obtaining good data.


The worst case on a rotating drive, if the data come clean on the 999th re-read, costs you about an additional quarter minute of elapsed time to re-read ONE block.


A work-around is to copy the data in much smaller batches, expecting to get a batch or two that take far longer or generate an error.


If you see the error -35 I/O error, that means the block was re-read 1,000 times and would not come clean. Divide that group in half and try to copy again. Keep dividing in half and trying again until you get down to the individual item causing the problem. That item probably can not be saved.

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Question marked as Top-ranking reply

Sep 16, 2020 12:18 PM in response to spyo97

If you are seeing elongated copy times, it suggests the source drive may have many Bad Blocks.


If the source drive is developing Bad Blocks, the standard resolution is to reread the data block, continuing to run the raw data through to drive's error-correction circuits, in hopes of obtaining good data.


The worst case on a rotating drive, if the data come clean on the 999th re-read, costs you about an additional quarter minute of elapsed time to re-read ONE block.


A work-around is to copy the data in much smaller batches, expecting to get a batch or two that take far longer or generate an error.


If you see the error -35 I/O error, that means the block was re-read 1,000 times and would not come clean. Divide that group in half and try to copy again. Keep dividing in half and trying again until you get down to the individual item causing the problem. That item probably can not be saved.

Sep 16, 2020 7:21 PM in response to spyo97

You can try checking the health of the external drive by using DriveDx. You will need to install a special USB driver so that DriveDx can access the health information on a USB drive. Even with this special driver not all USB controllers on external drives allow the necessary communication. If you can access the drive's health report, then post it here using the "Additional Text" icon which looks like a piece of paper.


If the drive is failing, then every failed attempt will likely make the failure even worse where even a professional data recovery service may not be able to recover the data. Standard utilities (even data recovery utilities) are unable to handle the errors produced by a failing drive. If the drive failure is minor and just beginning, then it may be possible to use Carbon Copy Cloner (CCC) to transfer the files since CCC will skip problem files, but only if there are just a few errors. Plus CCC allows you to easily select smaller sections to copy if you find out a section is more problematic. However, if CCC is running too slow and skipping more than a hand full of files, then I would abort the attempt.


Sep 16, 2020 11:36 PM in response to HWTech

That seemed to be the case!! Downloaded DriveDX and the problem actually wasn’t with the external, it was with the internal one I was attempting to copy to. The readout said it was pretty much completely failed. So looks like I’ll need a replacement. Is any 3.5” SATA 6.0gb/s compatible with my model?

External Hard Drive Not Copying Data

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