File: ddrescue.info,  Node: Examples,  Next: Direct disc access,  Prev: Optical media,  Up: Top

10 A small tutorial with examples
*********************************

This tutorial is for those already able to use the dd command. If you don't
know what dd is, better search the net for some introductory material about
dd and GNU ddrescue first.

   A failing drive tends to develop more and more errors as time passes.
Because of this, you should rescue the data from a drive as soon as you
notice the first error. Be diligent because every time a physically damaged
drive powers up and is able to output some data, it may be the very last
time that it ever will.

   You should make a copy of the failing drive with ddrescue, and then try
to repair the copy. If your data are really important, use the first copy
as a master for a second copy, and try to repair the second copy. If
something goes wrong, you have the master intact to try again.

   If you are trying to rescue a whole partition, first repair the copy with
e2fsck or some other tool appropriate for the type of partition you are
trying to rescue, then mount the repaired copy somewhere and try to recover
the files in it.

   If the drive is so damaged that the file system in the rescued partition
can't be repaired or mounted, you will have to browse the rescued data with
an hex editor and extract the desired parts by hand, or use a file recovery
tool like photorec.

   If the partition table is damaged, you may try to rescue the whole disc,
then try to repair the partition table and the partitions on the copy.

   If the damaged drive is not listed in '/dev', then you cannot rescue it.
At least not with ddrescue.

   *Note Optical media::, for rescue examples of CD-ROMs and DVDs.


Example 1: Fully automatic rescue of a whole disc with two ext2 partitions
in '/dev/sda' to '/dev/sdb'.
Note: you don't need to partition '/dev/sdb' beforehand, but if the
partition table on '/dev/sda' is damaged, you'll need to recreate it
somehow on '/dev/sdb'.

     ddrescue -f -r3 /dev/sda /dev/sdb mapfile
     fdisk /dev/sdb
     e2fsck -v -f /dev/sdb1
     e2fsck -v -f /dev/sdb2


Example 2: Rescue an ext2 partition in '/dev/sda2' to '/dev/sdb2'.
Note: you need to create the partition sdb2 with fdisk first. sdb2 should be
of appropriate type and size.

     ddrescue -f -n /dev/sda2 /dev/sdb2 mapfile
     ddrescue -d -f -r3 /dev/sda2 /dev/sdb2 mapfile
     e2fsck -v -f /dev/sdb2
     mount -t ext2 -o ro /dev/sdb2 /mnt
       (read rescued files from /mnt)


Example 3: While rescuing the whole drive '/dev/sda' to '/dev/sdb',
'/dev/sda' freezes up at position 12345678.

     ddrescue -f /dev/sda /dev/sdb mapfile         # /dev/sda freezes here
       (restart /dev/sda or reboot computer)
       (restart copy at a safe distance from the troubled sector)
     ddrescue -f -i 12350000 /dev/sda /dev/sdb mapfile
       (then copy backwards down to the troubled sector)
     ddrescue -f -R /dev/sda /dev/sdb mapfile


Example 4: While rescuing the whole drive '/dev/sda' to '/dev/sdb',
'/dev/sdb' fails and you have to rescue the data to a third drive,
'/dev/sdc'.

     ddrescue -f -n /dev/sda /dev/sdb mapfile1       # /dev/sdb fails here
     ddrescue -f -m mapfile1 /dev/sdb /dev/sdc mapfile2
     ddrescue -f -n /dev/sda /dev/sdc mapfile2
     ddrescue -d -f -r3 /dev/sda /dev/sdc mapfile2


Example 5: While rescuing a partition in '/dev/sda1' to the file 'hdimage',
'/dev/sda1' stops responding and begins returning read errors, causing
ddrescue to mark the rest of the partition as non-scraped.

     ddrescue -n /dev/sda1 hdimage mapfile          # /dev/sda1 fails here
       (restart /dev/sda or reboot computer)
     ddrescue -n -A -i -O /dev/sda1 hdimage mapfile
       (if /dev/sda1 fails again, restart /dev/sda or reboot computer and
        then repeat the above command as many times as needed until it
        succeeds.  is the position where the drive stopped responding)
     ddrescue -d -r3 /dev/sda1 hdimage mapfile


Example 6: While rescuing a partition in '/dev/sda1' to the file 'hdimage',
sda1 disappears from '/dev'.

     ddrescue -n /dev/sda1 hdimage mapfile          # /dev/sda1 fails here
       (restart /dev/sda or reboot computer and then repeat the above
        command as many times as needed until it succeeds)
     ddrescue -d -r3 /dev/sda1 hdimage mapfile


Example 7: While rescuing a partition in '/dev/sda1' to the file 'hdimage',
the partition table of '/dev/sda' becomes unreadable and the OS no longer
shows sda1 in '/dev'. The solution is to shift the mapfile and read the
rest of the partition sda1 from '/dev/sda'.
Note: you need to know the offset of the partition sda1 in the drive sda and
the size of sda1.

     ddrescue /dev/sda1 hdimage mapfile       # partition table fails here
     ddrescuelog --shift -o mapfile > shifted_mapfile
     ddrescue -i -o0 -s /dev/sda hdimage shifted_mapfile


Example 8: After rescuing a partition in '/dev/sda1' to the file 'hdimage',
expand 'hdimage' to copy the whole drive in '/dev/sda' without recopying
the already copied partition '/dev/sda1'. The solution is to shift the
mapfile, move the data of sda1 to its final position in 'hdimage', and then
read the rest of the data from '/dev/sda'.
Note: you need to know the offset of the partition sda1 in the drive sda and
the size of sda1.

     ddrescue /dev/sda1 hdimage mapfile             # rescue partition
     ddrescuelog --shift -o mapfile > shifted_mapfile
     ddrescue --same-file -o -s --reverse hdimage hdimage
     ddrescue /dev/sda hdimage shifted_mapfile      # rescue rest of drive