It’s very common for technicians to run into hard drives or files that are on the brink of failure or contain corrupted files that hang up traditional backup and transfer methods. Disk Utility can be used to create an image of a folder or drive, but tends to throw an input/output error at the slightest hesitation, like those caused by failing drives or corrupted files.
SuperDuper is much better at making disk images from failing drives or corrupted source material; while not the best tool for the job, it does seem to be the most versatile. I urge you to buy your own copy and support the developer of this fantastic tool: http://www.shirt-pocket.com.
Ditto is a command-line tool that will copy block by block the information from one directory (the source) to another (the destination). It’s very simple and does not care about hesitation from mechanical or logical failures. This said, it will not extract data from a hard drive that’s too far gone. I like to use Ditto in verbose mode, just so I can see that it’s working and how far along it is.
Many people avoid Terminal for fear of typing all those long commands and file paths. Not an unjustified fear because you can simply drag the source and destination right into the terminal window, and the paths will be automatically entered for you. Here’s how to use ditto my favorite way.
Assuming you have a terminal window open, simply type the following (but leave off the brackets):
ditto -v [source] [destination]
If you’re copying a folder on your Desktop to your Documents folder, it’d look like this:
ditto -v /Users/matt/Desktop/stuff/ Users/matt/Documents
The guide to using Ditto, and every other command line application, can be found by typing man x in terminal, where ‘x’ is the name of the application. So, for Ditto’s user guide, simply type man ditto and then press return.