Mac – Unable to create disk image using disk utility (Input/output error)

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."