I want to create a disk image of source 100.03 GB Ext Hard Disk Media on destination 5TB Lacie ST5000DX000-1H2170 there is greater than 1TB remaining on the destination disk. The Disk Utility progress windows displays the message

Creating Image Macintosh HD.dmg Reading whole disk (Apple_HFS : 0)…

with progress bar that moves up to about 50% before the following error message is displayed:

Unable to create Macintosh HD.dmg. (Input/output error).

Using Disk Utility, First Aid, Verify Disk, the volume "Macintosh HD" appears to be OK.

Is there a way to view any more detail than the console will provide? So that I can learn more about the error. It could be due to low power on the source drive - I am using a 2.5" HDD External enclosure (Mini G2 from Silicon P/L) requires 5VDC/0.5A usb to USB and power (host usb 1 - enclosure usb and enclosure round power split end cable) lead and I am using my MacBook Pro Retina, 13-inch, Late 2012 as the host USB port. The HD inside the enclosure is from an early model G4 Powerbook that was running Tiger OS X.

Other answers to input/output error suggest using DiskWarrior so I tried that, DiskWarrior fixed a bunch of flags and repaired permissions but when I ran disk utility again after that to create a new image it failed again for the same reason: input/output error.

Using the terminal command (from http://hints.macworld.com/article.php?story=20050302225659382)

dd bs=512 if=/dev/rXX# of=/some_dir/foo.dmg conv=noerror,sync

does produce an image but after completion it could not be opened (or mounted) due to a "no mountable file system."

  • Sounds like you have an irreparable error on the disk. You may want to dd the disk using the switch that tells dd to continue upon errors. If dd fails at I/O errors then you may want to take it as a lesson to improve your backup strategy, as the data at the error points may never be recoverable. – Kinnectus Jul 6 '14 at 8:24

Check your hard drive. I'd wager that you have bad sectors. I recently ran into the same issue because there were too many and the drive was close to failure.

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