Difference between revisions of "Ddrescue"

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(Other Resources)
 
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   genre = {{Disk imaging}} |
 
   genre = {{Disk imaging}} |
 
   license = {{GPL}} |
 
   license = {{GPL}} |
   website = [http://www.gnu.org/software/ddrescue/ddrescue.html ddrescue.html] |
+
   website = [http://www.gnu.org/software/ddrescue/ddrescue.html http://www.gnu.org/software/ddrescue/ddrescue.html] |
 
}}
 
}}
  
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== Installation ==
 
== Installation ==
=== Debian ===
+
 
The package 'ddrescue' actually is [[dd_rescue]], another dd-like program which does not maintain a recovery log.
+
=== Bootable CD ===
 +
ddrescue is available on bootable rescue cds such as SystemRescueCd http://www.sysresccd.org/Main_Page.
 +
=== Debian and Ubuntu ===
 +
The package 'ddrescue' in Debian and Ubuntu is actually [[dd_rescue]], another dd-like program which does not maintain a recovery log. The correct package is gddrescue.
 +
 
 +
Debian
 
<blockquote>
 
<blockquote>
 
aptitude install gddrescue
 
aptitude install gddrescue
 
</blockquote>
 
</blockquote>
 
+
Ubuntu
 +
<blockquote>
 +
sudo apt-get install gddrescue
 +
</blockquote>
 +
=== Gentoo ===
 +
<blockquote>
 +
emerge ddrescue
 +
</blockquote>
 
== Partition recovery ==
 
== Partition recovery ==
  
=== Kernel 2.6.3+ ===
+
=== Kernel 2.6.3+ & ddrescue 1.4+ ===
 
'ddrescue --direct' will open the input with the O_DIRECT option for uncached reads. 'raw devices' are not needed on newer kernels. For older kernels see below.
 
'ddrescue --direct' will open the input with the O_DIRECT option for uncached reads. 'raw devices' are not needed on newer kernels. For older kernels see below.
  
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You can now use ddrescue (or normal dd) to copy the imagefile to a new partition on a new disk. Use the appropriate filesystem checkers (fsck, CHKDSK) to try to fix errors caused by the bad blocks. Be sure to keep the imagefile around. Just in case the filesystem is severely broken, and datacarving tools like testdisk need to to be used on the original image.
 
You can now use ddrescue (or normal dd) to copy the imagefile to a new partition on a new disk. Use the appropriate filesystem checkers (fsck, CHKDSK) to try to fix errors caused by the bad blocks. Be sure to keep the imagefile around. Just in case the filesystem is severely broken, and datacarving tools like testdisk need to to be used on the original image.
  
=== Before kernel 2.6.3, and 2.4.x ===
+
=== Before linux kernel 2.6.3 / 2.4.x ===
 
In 2.6.3 the 'raw device' has been marked obsolete. On later kernels ddrescue will use O_DIRECT on the input to do uncached reads.
 
In 2.6.3 the 'raw device' has been marked obsolete. On later kernels ddrescue will use O_DIRECT on the input to do uncached reads.
  
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Example 1: Rescue an ext2 partition in /dev/hda2 to /dev/hdb2
 
Example 1: Rescue an ext2 partition in /dev/hda2 to /dev/hdb2
 +
 +
'''Please Note:''' This will overwrite ALL data on the partition you are copying to. If you do not want to do that, rather create an image of the partition to be rescued.
 
<blockquote>
 
<blockquote>
 
ddrescue -r3 /dev/hda2 /dev/hdb2 logfile<br>
 
ddrescue -r3 /dev/hda2 /dev/hdb2 logfile<br>
Line 98: Line 112:
 
</blockquote>
 
</blockquote>
 
write cdimage to a blank CD-ROM
 
write cdimage to a blank CD-ROM
 +
 +
 +
This example is derived from the ddrescue manual.
 +
 +
Example 3: Rescue an entire hard disk /dev/sda to another disk /dev/sdb
 +
 +
copy the error free areas first
 +
ddrescue -n /dev/sda /dev/sdb rescue.log
 +
attempt to recover any bad sectors
 +
ddrescue -r 1 /dev/sda /dev/sdb rescue.log
 +
 +
== Options ==
 +
 +
-h, --help
 +
    display this help and exit
 +
-V, --version
 +
    output version information and exit
 +
-b, --block-size=<bytes>
 +
    hardware block size of input device [512]
 +
-B, --binary-prefixes
 +
    show binary multipliers in numbers [default SI]
 +
-c, --cluster-size=<blocks>
 +
    hardware blocks to copy at a time [128]
 +
-C, --complete-only
 +
    do not read new data beyond logfile limits
 +
-d, --direct
 +
    use direct disc access for input file
 +
-D, --synchronous
 +
    use synchronous writes for output file
 +
-e, --max-errors=<n>
 +
    maximum number of error areas allowed
 +
-F, --fill=<types>
 +
    fill given type areas with infile data (?*/-+)
 +
-g, --generate-logfile
 +
    generate approximate logfile from partial copy
 +
-i, --input-position=<pos>
 +
    starting position in input file [0]
 +
-n, --no-split
 +
    do not try to split or retry error areas
 +
-o, --output-position=<pos>
 +
    starting position in output file [ipos]
 +
-q, --quiet
 +
    quiet operation
 +
-r, --max-retries=<n>
 +
    exit after given retries (-1=infinity) [0]
 +
-R, --retrim
 +
    mark all error areas as non-trimmed
 +
-s, --max-size=<bytes>
 +
    maximum size of data to be copied
 +
-S, --sparse
 +
    use sparse writes for output file
 +
-t, --truncate
 +
    truncate output file
 +
-v, --verbose
 +
    verbose operation
 +
 +
Numbers may be followed by a multiplier: b = blocks, k = kB = 10^3 = 1000, Ki = KiB = 2^10 = 1024, M = 10^6, Mi = 2^20, G = 10^9, Gi = 2^30, etc...
 +
  
 
== Cygwin ==
 
== Cygwin ==
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* [[dd_rescue]]
 
* [[dd_rescue]]
 
* [[sdd]]
 
* [[sdd]]
 +
 +
== Other Resources ==
 +
[http://pfuender.net/?p=80| Useful code-snippets for DDrescue]
 +
 +
[http://www.myfixlog.com/fix.php?fid=21| Tutorial for beginners that guides through the process of imaging a hard drive with DDrescue and mounting it in Windows, using free software.]

Latest revision as of 12:03, 9 January 2011

ddrescure
Maintainer: Antonio Diaz Diaz
OS: Linux
Genre: Disk imaging
License: GPL
Website: http://www.gnu.org/software/ddrescue/ddrescue.html

ddrescue is a raw disk imaging tool that "copies data from one file or block device to another, trying hard to rescue data in case of read errors." The application is developed as part of the GNU project and has written with UNIX/Linux in mind.

ddrescue and dd_rescue are completely different programs which share no development between them. The two projects are not related in any way except that they both attempt to enhance the standard dd tool and coincidentally chose similar names for their new programs.

From the ddrescue info pages:

GNU ddrescue is a data recovery tool. It copies data from one file or block device (hard disc, cdrom, etc) to another, trying hard to rescue data in case of read errors.

Ddrescue 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.

The basic operation of ddrescue is fully automatic. That is, you don't have to wait for an error, stop the program, read the log, run it in reverse mode, etc.

If you use the logfile feature of 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.

Automatic merging of backups: If you have two or more damaged copies of a file, cdrom, etc, and run ddrescue on all of them, one at a time, with the same output file, you will probably obtain a complete and error-free file. This is so because the probability of having damaged areas at the same places on different input files is very low. Using the logfile, only the needed blocks are read from the second and successive copies.

Installation

Bootable CD

ddrescue is available on bootable rescue cds such as SystemRescueCd http://www.sysresccd.org/Main_Page.

Debian and Ubuntu

The package 'ddrescue' in Debian and Ubuntu is actually dd_rescue, another dd-like program which does not maintain a recovery log. The correct package is gddrescue.

Debian

aptitude install gddrescue

Ubuntu

sudo apt-get install gddrescue

Gentoo

emerge ddrescue

Partition recovery

Kernel 2.6.3+ & ddrescue 1.4+

'ddrescue --direct' will open the input with the O_DIRECT option for uncached reads. 'raw devices' are not needed on newer kernels. For older kernels see below.

First you copy as much data as possible, without retrying or splitting sectors:

ddrescue --no-split /dev/hda1 imagefile logfile

Now let it retry previous errors 3 times, using uncached reads:

ddrescue --direct --max-retries=3 /dev/hda1 imagefile logfile

If that fails you can try again but retrimmed, so it tries to reread full sectors:

ddrescue --direct --retrim --max-retries=3 /dev/hda1 imagefile logfile

You can now use ddrescue (or normal dd) to copy the imagefile to a new partition on a new disk. Use the appropriate filesystem checkers (fsck, CHKDSK) to try to fix errors caused by the bad blocks. Be sure to keep the imagefile around. Just in case the filesystem is severely broken, and datacarving tools like testdisk need to to be used on the original image.

Before linux kernel 2.6.3 / 2.4.x

In 2.6.3 the 'raw device' has been marked obsolete. On later kernels ddrescue will use O_DIRECT on the input to do uncached reads.

First you copy as much data as possible, without retrying or splitting sectors:

ddrescue --no-split /dev/hda1 imagefile logfile

Now change over to raw device access. Let it retry previous errors 3 times, don't read past last block in logfile:

modprobe raw
raw /dev/raw/raw1 /dev/hda1
ddrescue --max-retries=3 --complete-only /dev/raw/raw1 imagefile logfile

If that fails you can try again (still using raw) but retrimmed, so it tries to reread full sectors:

ddrescue --retrim --max-retries=3 --complete-only /dev/raw/raw1 imagefile logfile

You can now use ddrescue (or normal dd) to copy the imagefile to a new partition on a new disk. Use the appropriate filesystem checkers (fsck, CHKDSK) to try to fix errors caused by the bad blocks. Be sure to keep the imagefile around. Just in case the filesystem is severely broken, and datacarving tools like testdisk need to to be used on the original image.

At the end you may want to unbind the raw device:

raw /dev/raw/raw1 0 0

Examples

These two examples are taken directly from the ddrescue info pages.

Example 1: Rescue an ext2 partition in /dev/hda2 to /dev/hdb2

Please Note: This will overwrite ALL data on the partition you are copying to. If you do not want to do that, rather create an image of the partition to be rescued.

ddrescue -r3 /dev/hda2 /dev/hdb2 logfile
e2fsck -v -f /dev/hdb2
mount -t ext2 -o ro /dev/hdb2 /mnt

Example 2: Rescue a CD-ROM in /dev/cdrom

ddrescue -b 2048 /dev/cdrom cdimage logfile

write cdimage to a blank CD-ROM


This example is derived from the ddrescue manual.

Example 3: Rescue an entire hard disk /dev/sda to another disk /dev/sdb

copy the error free areas first

ddrescue -n /dev/sda /dev/sdb rescue.log

attempt to recover any bad sectors

ddrescue -r 1 /dev/sda /dev/sdb rescue.log

Options

-h, --help
   display this help and exit 
-V, --version
   output version information and exit 
-b, --block-size=<bytes>
   hardware block size of input device [512] 
-B, --binary-prefixes
   show binary multipliers in numbers [default SI] 
-c, --cluster-size=<blocks>
   hardware blocks to copy at a time [128] 
-C, --complete-only
   do not read new data beyond logfile limits 
-d, --direct
   use direct disc access for input file 
-D, --synchronous
   use synchronous writes for output file 
-e, --max-errors=<n>
   maximum number of error areas allowed 
-F, --fill=<types>
   fill given type areas with infile data (?*/-+) 
-g, --generate-logfile
   generate approximate logfile from partial copy 
-i, --input-position=<pos>
   starting position in input file [0] 
-n, --no-split
   do not try to split or retry error areas 
-o, --output-position=<pos>
   starting position in output file [ipos] 
-q, --quiet
   quiet operation 
-r, --max-retries=<n>
   exit after given retries (-1=infinity) [0] 
-R, --retrim
   mark all error areas as non-trimmed 
-s, --max-size=<bytes>
   maximum size of data to be copied 
-S, --sparse
   use sparse writes for output file 
-t, --truncate
   truncate output file 
-v, --verbose
   verbose operation

Numbers may be followed by a multiplier: b = blocks, k = kB = 10^3 = 1000, Ki = KiB = 2^10 = 1024, M = 10^6, Mi = 2^20, G = 10^9, Gi = 2^30, etc...


Cygwin

As of release 1.4-rc1, it can be compiled directly in Cygwin Out of the Box. Precompiled packages are available in the Cygwin distribution. This makes it usable natively on Windows systems.

See also

Other Resources

Useful code-snippets for DDrescue

Tutorial for beginners that guides through the process of imaging a hard drive with DDrescue and mounting it in Windows, using free software.