External Hard Drive Not Copying Data

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.

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.

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