I am trying to copy a 200GB dmg file between two disks (one firewire, one local) and see this error:

The Finder can’t complete the operation because some data in “mbp_18_06_2011.dmg” can’t be read or written.
(Error code -36)

How can I debug / fix?

2 Answers 2


You can try copying the data using Terminal

Type in sudo ditto ~/sourcefile ~/Destination

Replace "~/sourcefile" by dragging the file you want to copy into the terminal window which will autofill, and do the same with the "~/destination"

Alternatively: sudo ditto -V ~/sourcefile ~/Desktop This will show you progress and any errors as the files are being copied

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  • thanks. would the -nocache option prevent any temporary copies being created? The operation failed with a similar error. BTW, its just one file, ~200GB
    – codecowboy
    Commented Mar 14, 2014 at 14:08
  • ditto: /Volumes/Backups2011/Old MPB/./mbp_18_06_2011.dmg: Input/output error
    – codecowboy
    Commented Mar 14, 2014 at 15:09
  • Hello, sorry for the late reply. I/O errors means the hard drive has bad sectors hence the reason why you can't successfully copy the data across.
    – Maximus
    Commented Apr 1, 2014 at 12:11

If the dmg is mounted, you'll get that error when trying to copy it I believe. Eject/unmount the dmg file first and try to copy it.

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