How to rescue your data on a failing hard drive with dd_rescue

I just got done answering this question for someone at work:

What was that app that allowed you to duplicate the failing hard drive?

So I figured, why not put it out there for the Internets to see?

It’s the dd_rescue command within Knoppix. (I’ve always used 5.0 or 6.1 – I think dd_rescue is still included in version 7)

You need to boot to the Knoppix CD/DVD and run dd_rescue on the DISK, not the PARTITION.


dd_rescue /dev/sda /dev/sdb

Given that /dev/sda is your source drive, and /dev/sdb is the destination drive.

You can check your disk configuration like this:

fdisk -l

Read the output from there to see which disk is which. Your best bet is to use a sanitized drive as the destination so it’s easier to tell which disk has stuff on it and which doesn’t.

Since this is all command line, I HIGHLY recommend running a practice job using data that doesn’t matter before going forward with real data. This process can easily ruin good data if you have the command backwards.

Additional switches:

You can use these switches to “sandwich” a bad spot on the drive and pick up as much data as possible.

-s defines the start position.
Ex: (will start at 15G and go forwards)

dd_rescue –s 15G /dev/sda /dev/sdb

-r defines working from front to back
Ex: (will start at 15G and go in reverse, back to the beginning of the drive)
(-r does not use DMA buffer, which can increase error correcting abilities)

dd_rescue –r –s 15G /dev/sda /dev/sdb

Mike Erps

Michael Erps currently provides IT support and consulting to gov’t contractors in D.C. He is also interested in Internet Marketing and helping others build the online presence they are looking for. You can find him on