gddrescue: a tool for recovering data from damaged media

December 12th, 2007 edited by Tincho

Entry submitted by John Carlyle-Clarke. DPOTD needs your help, please contribute!

I wanted to recover data from a failing hard drive, and asked on IRC if any good tools existed for Ubuntu. Someone pointed me towards GNU ddrescue (named gddrescue in Debian and Ubuntu), which is designed for rescuing data from any file or block device.

Don’t confuse this with dd_rescue (package name ddrescue). GNU rescue is a better tool.

The GNU site describes GNU ddrescue as a data recovery tool, and lists these features:

  • It copies data from one file or block device (hard disc, CD-ROM, etc) to another, trying hard to rescue data in case of read errors.
  • It does not truncate the output file if not asked to, so every time you run it on the same output file, it tries to fill in the gaps.
  • It is designed to be fully automatic.
  • If you use the log file feature of GNU ddrescue, the data is rescued very efficiently (only the needed blocks are read). Also you can interrupt the rescue at any time and resume it later at the same point.
  • The log file is periodically saved to disc. So in case of a crash you can resume the rescue with little recopying.
  • If you have two or more damaged copies of a file, CD-ROM, etc, and run GNU ddrescue on all of them, one at a time, with the same output file, you will probably obtain a complete and error-free file. The probability of having damaged areas at the same places on different input files is very low. Using the log file, only the needed blocks are read from the second and successive copies.
  • The same log file can be used for multiple commands that copy different areas of the file, and for multiple recovery attempts over different subsets.

The algorithm of GNU ddrescue is as follows:

  1. Optionally read a log file describing the status of a multi-part or previously interrupted rescue.
  2. Read the non-damaged parts of the input file, skipping the damaged areas, until the requested size is reached, or until interrupted by the user.
  3. Try to read the damaged areas, splitting them into smaller pieces and reading the non-damaged pieces, until the hardware block size is reached, or until interrupted by the user.
  4. Try to read the damaged hardware blocks until the specified number of retries is reached, or until interrupted by the user.
  5. Optionally write a log file for later use.

To use it, you need to install gddrescue, but it is invoked as ddrescue. This is confusing, but it’s because dd_rescue had already taken the name.

The syntax is simple and the man and info documents are pretty good. Here is an example session with a data CD (no errors found).

$ ddrescue -v /dev/cdrom Recovered.iso ddrescue.log

About to copy 101763 kBytes from /dev/cdrom to Recovered.iso
    Starting positions: infile = 0 B,  outfile = 0 B
    Copy block size: 128 hard blocks
Hard block size: 512 bytes
Max_retries: 0    Split: yes    Truncate: no

Press Ctrl-C to interrupt
Initial status (read from logfile)
rescued:         0 B,  errsize:       0 B,  errors:       0
Current status
rescued:   101763 kB,  errsize:       0 B,  current rate:    3801 kB/s
   ipos:   101711 kB,   errors:       0,    average rate:    2702 kB/s
   opos:   101711 kB

Useful links:-

Related software:-

gddrescue is available in Debian since Etch, and in Ubuntu since Edgy. It was started by Antonio Diaz Diaz in 2004.

Posted in Debian, Ubuntu |

6 Responses

  1. Eddahbi Karim Says:

    Another related multiplatform free software is TestDisk ( ).

    It can recover files from multiple file systems and disk configurations (RAID, LVM, …).

    I already tried it successfully on two machines.

    There’s another software named PhotoRec, distributed on the same website, but is more oriented on multimedia files, hence its name

  2. N. Nobelis Says:

    Very useful : thanks !!!

  3. Sitaram Says:

    Some more notes from my personal tipswiki:

    - for CD-ROMs you should probably specific “-b 2048″

    - if the disk is failing fast and you want to get the most data out of it on the first try, you should probably use “-n” on the first run. This will avoid splitting error areas. Subsequent runs can use “-r1″ or “-r3″, without “-n”, to retry those error areas.

  4. Matthas Maisenbacher Says:

    I’d like to mention dvdisaster.
    It’s designed for preventing CDs/DVDs fom getting unreadable.
    But it can also be used to recover from disks if you did no prevention. In fact I most often use ist to create images from disks.
    It also has a good algorithm,
    it offers the ability to recover from different drives, maybe reading different parts of the disk and so completing the image. And it has a nice GUI.

    It’s in Debian since etch.

    Homepage is

  5. ThE_TemPLaR Says:

    Another related softwares are TestDisk and PhotoRec which are multiplatform.

    The homepage of these projects are :

  6. Andrew Says:

    Thanks for providing nice article on data recovery. I have used Stellar Phoenix Windows data recovery to recover my lost partition.This is very good software you can try it.