Difference between pages "Ddrescue" and "File:3-bb9320-ScreenRemoval.jpg"

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{{Infobox_Software |
 
  name = ddrescure |
 
  maintainer = [[Antonio Diaz Diaz]]|
 
  os = {{Linux}}|
 
  genre = {{Disk imaging}} |
 
  license = {{GPL}} |
 
  website = [http://www.gnu.org/software/ddrescue/ddrescue.html 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:
 
<blockquote>
 
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.<br><br>
 
 
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.<br><br>
 
 
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.<br><br>
 
 
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.<br><br>
 
 
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.
 
</blockquote>
 
 
== 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
 
<blockquote>
 
aptitude install gddrescue
 
</blockquote>
 
Ubuntu
 
<blockquote>
 
sudo apt-get install gddrescue
 
</blockquote>
 
=== Gentoo ===
 
<blockquote>
 
emerge ddrescue
 
</blockquote>
 
== 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:
 
<blockquote>
 
ddrescue --no-split /dev/hda1 imagefile logfile
 
</blockquote>
 
 
Now let it retry previous errors 3 times, using uncached reads:
 
<blockquote>
 
ddrescue --direct --max-retries=3 /dev/hda1 imagefile logfile
 
</blockquote>
 
 
If that fails you can try again but retrimmed, so it tries to reread full sectors:
 
<blockquote>
 
ddrescue --direct --retrim  --max-retries=3 /dev/hda1 imagefile logfile
 
</blockquote>
 
 
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:
 
<blockquote>
 
ddrescue --no-split /dev/hda1 imagefile logfile
 
</blockquote>
 
 
Now change over to raw device access. Let it retry previous errors 3 times, don't read past last block in logfile:
 
<blockquote>
 
modprobe raw<br>
 
raw /dev/raw/raw1 /dev/hda1<br>
 
ddrescue --max-retries=3 --complete-only /dev/raw/raw1 imagefile logfile
 
</blockquote>
 
 
If that fails you can try again (still using raw) but retrimmed, so it tries to reread full sectors:
 
<blockquote>
 
ddrescue --retrim --max-retries=3 --complete-only /dev/raw/raw1 imagefile logfile
 
</blockquote>
 
 
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:
 
<blockquote>
 
raw /dev/raw/raw1 0 0
 
</blockquote>
 
 
== 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.
 
<blockquote>
 
ddrescue -r3 /dev/hda2 /dev/hdb2 logfile<br>
 
e2fsck -v -f /dev/hdb2<br>
 
mount -t ext2 -o ro /dev/hdb2 /mnt<br>
 
</blockquote>
 
 
Example 2: Rescue a CD-ROM in /dev/cdrom
 
<blockquote>
 
ddrescue -b 2048 /dev/cdrom cdimage logfile
 
</blockquote>
 
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]] [http://en.wikipedia.org/wiki/Out_of_the_box Out of the Box]. Precompiled packages are available in the [http://cygwin.com/packages/ Cygwin distribution]. This makes it usable natively on [[Windows]] systems.
 
 
== See also ==
 
 
* [[aimage]]
 
* [[Blackbag]]
 
* [[dcfldd]]
 
* [[dd]]
 
* [[dd_rescue]]
 
* [[sdd]]
 
 
== Other Resources ==
 
[http://pfuender.net/?p=80|Useful code-snippets for DDrescue]
 

Latest revision as of 12:28, 30 October 2013