Cyclic redundancy check on external hard drive

There are a number of programs that will read all the sectors of the drive and try to recover whatever files are found. If you search the forum for "drive recovery," you will see some suggestions.

These programs will usually scan the disk and recover a sample file for free, then require about $100 to unlock to recover the files. Since professional recovery services run in the thousands of dollars, these programs are well worth a try.

Two caveats: Make sure that nothing is allowed to write to the disk, and don't try to format it. This will almost certainly overwrite the data that you need, which is now considered to be free space.

The second caveat: backup frequently.

There are some free options. Disk Copy is one... http://www.easeus.com/disk-copy/

The idea is to try and take a sector by sector image of your failing drive onto a new drive and then try to access your data off the new drive image.

It may also help to first extract the disk from the USB enclosure and connect it directly to a SATA port.

FDR: wouldn't copying a corrupt disk yield a corrupt disk?

Sectors that are unreadable on the failing drive obviously can not be copied over to a new drive. So there will be some degree of corruption.

However in many cases the number of unreadable sectors is relatvely small. And it is often possible to recover data by operating on the image.

For example on a recent case a drive suffering from bad sectors, of the 150,000 files on the drive all were recovered except for 200 files which suffered some degree of corruption. So although it's not perfect it's certainly a worthwhile result.