Difference between revisions of "Disk cloning"

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[[Category:Data compression and archiving]]
 
[[Category:Data compression and archiving]]
 
[[Category:System recovery]]
 
[[Category:System recovery]]
[[it:Disk Cloning]]
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[[it:Disk cloning]]
[[ru:Disk Cloning]]
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[[ja:ディスクのクローン]]
[[tr:Disk_klonlama]]
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[[ru:Disk cloning]]
Disk cloning is the process of making an image of a partition or an entire hard drive. This can be useful both for copying the drive to other computers and for backup/recovery purposes.
+
[[tr:Disk klonlama]]
 +
[[zh-CN:Disk cloning]]
 +
Disk cloning is the process of making an image of a partition or of an entire hard drive. This can be useful for copying the drive to other computers and for [[backup]] and [[File recovery|recovery]] purposes.
  
===Using dd===
+
== Using dd ==
The dd command is a simple, yet versatile and powerful tool. It can be used to copy from source to destination, block-by-block, regardless of their filesystem types or operating systems. A convenient method is to use dd from a live environment, as in a livecd.
+
{{Warning|As with any command of this type, you should be very cautious when using it; it can destroy data. Remember the order of input file <nowiki>(if=) and output file (of=) and do not reverse them! Always ensure that the destination drive or partition (of=) is of equal or greater size than the source (if=).</nowiki>}}
+
====Cloning a partition====
+
From physical disk /dev/sda, partition 1, to physical disk /dev/sdb, partition 1.
+
dd if=/dev/sda1 of=/dev/sdb1 bs=4096 conv=notrunc,noerror
+
If output file '''''of''''' (sdb1 in the example) does not exist, dd will start at the beginning of the disk and create it.
+
  
====Cloning an entire hard disk====
+
The ''dd'' command is a simple, yet versatile and powerful tool. It can be used to copy from source to destination, block-by-block, regardless of their filesystem types or operating systems. A convenient method is to use ''dd'' from a live environment, as in a Live CD.
From physical disk /dev/sda to physical disk /dev/sdb
+
dd if=/dev/sda of=/dev/sdb bs=4096 conv=notrunc,noerror
+
This will clone the entire drive, including MBR (and therefore bootloader), all partitions, UUID's, and data.
+
*''notrunc'' or 'do not truncate' maintains data integrity by instructing dd not to truncate any data.
+
*''noerror'' instructs dd to continue operation, ignoring all input errors. Default behavior for dd is to halt at any error.
+
*''bs=4096'' sets the block size to 4k, an optimal size for hard disk read/write efficiency and therefore, cloning speed.
+
  
====Backing up the MBR====
+
{{Warning|As with any command of this type, you should be very cautious when using it; it can destroy data. Remember the order of input file ({{ic|1=if=}}) and output file ({{ic|1=of=}}) and do not reverse them! Always ensure that the destination drive or partition ({{ic|1=of=}}) is of equal or greater size than the source ({{ic|1=if=}}).
 +
}}
 +
 
 +
{{Accuracy|1=Are the conv= options safe to use? See:|section=remove conv sync noerror}}
 +
 
 +
=== Cloning a partition ===
 +
 
 +
From physical disk {{ic|/dev/sda}}, partition 1, to physical disk {{ic|/dev/sdb}}, partition 1.
 +
# dd if=/dev/sda1 of=/dev/sdb1 bs=64K conv=noerror,sync
 +
 
 +
{{Warning|If output file {{ic|1=of=}} ({{ic|sdb1}} in the example) does not exist, ''dd'' will create a file with this name and will start filling up your root file system!}}
 +
 
 +
=== Cloning an entire hard disk ===
 +
 
 +
From physical disk {{ic|/dev/sd''X''}} to physical disk {{ic|/dev/sd''Y''}}
 +
# dd if=/dev/sd''X'' of=/dev/sd''Y'' bs=64K conv=noerror,sync
 +
 
 +
This will clone the entire drive, including the MBR (and therefore bootloader), all partitions, UUIDs, and data.
 +
* {{ic|noerror}} instructs ''dd'' to continue operation, ignoring all read errors. Default behavior for ''dd'' is to halt at any error.
 +
* {{ic|sync}} fills input blocks with zeroes if there were any read errors, so data offsets stay in sync.
 +
* {{ic|1=bs=}} sets the block size. Defaults to 512 bytes, which is the "classic" block size for hard drives since the early 1980s, but is not the most convenient. Use a bigger value, 64K or 128K. Also, please read the warning below, because there is more to this than just "block sizes" -it also influences how read errors propagate. See [http://www.mail-archive.com/eug-lug@efn.org/msg12073.html] and [http://blog.tdg5.com/tuning-dd-block-size/] for details and to figure out the best bs value for your use case.
 +
 
 +
{{Warning|The block size you specify influences how read errors are handled. Read below. For data recovery, use [[#Using ddrescue|ddrescue]].}}
 +
 
 +
The ''dd'' utility technically has an "input block size" (IBS) and an "output block size" (OBS). When you set {{ic|bs}}, you effectively set both IBS and OBS. Normally, if your block size is, say, 1 MiB, ''dd'' will read 1024*1024 bytes and write as many bytes. But if a read error occurs, things will go wrong. Many people seem to think that ''dd'' will "fill up read errors with zeroes" if you use the {{ic|noerror,sync}} options, but this is not what happens. ''dd'' will, according to documentation, fill up the OBS to IBS size ''after completing its read'', which means adding zeroes at the ''end'' of the block. This means, for a disk, that effectively the whole 1 MiB would become messed up because of a single 512 byte read error in the beginning of the read: 12ERROR89 would become 128900000 instead of 120000089.
 +
 
 +
If you are positive that your disk does not contain any errors, you could proceed using a larger block size, which will increase the speed of your copying several fold. For example, changing bs from 512 to 64K changed copying speed from 35 MB/s to 120 MB/s on a simple Celeron 2.7 GHz system. But keep in mind that read errors on the source disk will end up as ''block errors'' on the destination disk, i.e. a single 512-byte read error will mess up the whole 64 KiB output block.
 +
 
 +
{{Tip|If you would like to view ''dd'' progressing, use the {{ic|1=status=progress}} option. See [[dd]] for details.}}
 +
 
 +
{{Note|
 +
* To regain unique UUIDs of an ''ext2/3/4'' filesystem, use {{ic|tune2fs /dev/sd''XY'' -U random}} on every partition.
 +
* Partition table changes from ''dd'' are not registered by the kernel. To notify of changes without rebooting, use a utility like ''partprobe'' (part of [[GNU Parted]]).
 +
}}
 +
 
 +
=== Backing up the MBR ===
  
 
The MBR is stored in the the first 512 bytes of the disk. It consist of 3 parts:
 
The MBR is stored in the the first 512 bytes of the disk. It consist of 3 parts:
#The first 446 bytes contain the boot loader.
 
#The next 64 bytes contain the partition table (4 entries of 16 bytes each, one entry for each primary partition).
 
#The last 2 bytes contain an identifier
 
  
To save the MBR into the file "mbr.img":
+
# The first 446 bytes contain the boot loader.
  # dd if=/dev/hda of=/mnt/sda1/mbr.img bs=512 count=1
+
# The next 64 bytes contain the partition table (4 entries of 16 bytes each, one entry for each primary partition).
 +
# The last 2 bytes contain an identifier
  
To restore (be careful : this could destroy your existing partition table and with it access to all data on the disk):
+
To save the MBR as {{ic|mbr.img}}:
  # dd if=/mnt/sda1/mbr.img of=/dev/hda
+
# dd if=/dev/sdX of=/path/to/mbr_file.img bs=512 count=1
 +
 
 +
To restore (be careful: this could destroy your existing partition table and with it access to all data on the disk):
 +
# dd if=/path/to/mbr_file.img of=/dev/sdX
  
 
If you only want to restore the boot loader, but not the primary partition table entries, just restore the first 446 bytes of the MBR:  
 
If you only want to restore the boot loader, but not the primary partition table entries, just restore the first 446 bytes of the MBR:  
  # dd if=/mnt/sda1/mbr.img of=/dev/hda bs=446 count=1
+
# dd if=/path/to/mbr_file.img of=/dev/sdX bs=446 count=1
  
To restore only the partition table, one must use  
+
To restore only the partition table, one must use:
  # dd if=/mnt/sda1/mbr.img of=/dev/hda bs=1 skip=446 count=64
+
# dd if=/path/to/mbr_file.img of=/dev/sdX bs=1 skip=446 count=64
  
You can also get the MBR from a full dd disk image.
+
You can also get the MBR from a full dd disk image:
  #dd if=/path/to/disk.img of=/mnt/sda1/mbr.img bs=512 count=1
+
# dd if=/path/to/disk.img of=/path/to/mbr_file.img bs=512 count=1
  
====Create disk image====
+
=== Create disk image ===
1. Boot from a liveCD or liveUSB.
+
 
 +
1. Boot from a live media.
  
 
2. Make sure no partitions are mounted from the source hard drive.
 
2. Make sure no partitions are mounted from the source hard drive.
Line 52: Line 79:
  
 
4. Backup the drive.  
 
4. Backup the drive.  
  # dd if=/dev/hda conv=sync,noerror bs=64K | gzip -c  > /mnt/sda1/hda.img.gz
+
# dd if=/dev/sd''X'' conv=sync,noerror bs=64K | gzip -c  > ''/path/to/backup.img.gz''
  
5. Save extra information about the drive geometry necessary in order to interpret the partition table stored within the image. The most important of which is the cylinder size.
+
If necessary (e.g. when the format of the external HD is FAT32) split the disk image in volumes (see also the ''split'' man pages).
  # fdisk -l /dev/hda > /mnt/sda1/hda_fdisk.info
+
  
'''NOTE:''' You may wish to use a block size (bs=) that is equal to the amount of cache on the HD you are backing up. For example, bs=8192K works for an 8MB cache. The 64K mentioned in this article is better than the default bs=512 bytes, but it will run faster with a larger bs=.
+
# dd if=/dev/sd''X'' conv=sync,noerror bs=64K | gzip -c | split -a3 -b2G - ''/path/to/backup.img.gz''
  
====Restore system====
+
If there is not enough disk space locally, you may send the image through ssh:
 +
 
 +
# dd if=/dev/sd''X'' conv=sync,noerror bs=64K | gzip -c | ssh user@local dd of=backup.img.gz
 +
 
 +
5. Save extra information about the drive geometry necessary in order to interpret the partition table stored within the image. The most important of which is the cylinder size.
 +
 
 +
# fdisk -l /dev/sd''X'' > ''/path/to/list_fdisk.info''
 +
 
 +
{{Note|You may wish to use a block size ({{ic|1=bs=}}) that is equal to the amount of cache on the HD you are backing up. For example, {{ic|1=bs=8192K}} works for an 8 MiB cache. The 64 KiB mentioned in this article is better than the default {{ic|1=bs=512}} bytes, but it will run faster with a larger {{ic|1=bs=}}.}}
 +
 
 +
=== Restore system ===
  
 
To restore your system:
 
To restore your system:
  # gunzip -c /mnt/sda1/hda.img.gz | dd of=/dev/hda
+
# gunzip -c ''/path/to/backup.img.gz'' | dd of=/dev/sd''X''
===Using cp===
+
 
The cp program can be used to clone a disk, one partition at a time. An advantage to using cp is that the filesystem type of the destination partition(s) may be the same or different than the source. For safety, perform the process from a live environment.
+
When the image has been split, use the following instead:
 +
# cat ''/path/to/backup.img.gz*'' | gunzip -c | dd of=/dev/sd''X''
 +
 
 +
== Using ddrescue ==
 +
''ddrescue'' is a tool designed for cloning and recovering data. It copies data from one file or block device (hard disc, cdrom, etc) to another, trying to rescue the good parts first in case of read errors, to maximize the recovered data.
 +
 
 +
To clone a faulty or dying drive, run ddrescue twice. First round, copy every block without read error and log the errors to rescue.log.
 +
 
 +
# ddrescue -f -n /dev/sdX /dev/sdY rescue.log
 +
 
 +
Second round, copy only the bad blocks and try 3 times to read from the source before giving up.
 +
 
 +
# ddrescue -d -f -r3 /dev/sdX /dev/sdY rescue.log
 +
 
 +
Now you can check the file system for corruption and mount the new drive.
 +
 
 +
# fsck -f /dev/sdY
 +
 
 +
== Disk cloning software ==
 +
 
 +
These applications allow easy backup of entire filesystems and recovery in case of failure, usually in the form of a Live CD or USB drive. They contain complete system images from one or more specific points in time and are frequently used to record known good configurations.
 +
 
 +
See also [[Synchronization and backup programs]] for other applications that can take full system snapshots, among other functionality.
 +
 
 +
* {{App|[[wikipedia:Acronis_True_Image|Acronis True Image]]|Commercial disk cloner for Windows. It allows you to create a live (from within Windows), so you do not need a working Windows install on the actual machine to use it. After registration of the Acronis software on their website, you will be able to download a Linux-based Live CD and/or plugins for BartPE for creation of the Windows-based live CD. It can also create a WinPE Live CD based on Windows. The created ISO Live CD image by Acronis doesn't have the [http://www.syslinux.org/wiki/index.php/Isohybrid hybrid boot] ability and cannot be written to USB storage as a raw file.|http://www.acronis.com/products/trueimage/|}}
 +
 
 +
* {{App|Arch Backup|A trivial backup script with simple configuration.
 +
** Configurable compression method.
 +
** Multiple backup targets.
 +
|http://code.google.com/p/archlinux-stuff/|{{AUR|arch-backup}}}}
 +
 
 +
* {{App|[[Wikipedia:Clonezilla|Clonezilla]]|A disaster recovery, disk cloning, disk imaging and deployment solution.
 +
** Boots from live CD, USB flash drive, or PXE server.
 +
** Supports ext2, ext3, ext4, reiserfs, reiser4, xfs, jfs, btrfs FAT32, NTFS, HFS+ and others.
 +
** Uses Partclone (default), Partimage (optional), ntfsclone (optional), or dd to image or clone a partition.
 +
** Multicasting server to restore to many machines at once.
 +
** Included on the Arch Linux installation media.
 +
|http://clonezilla.org/|{{Pkg|clonezilla}}}}
 +
 
 +
* {{App|FSArchiver|A safe and flexible file-system backup and deployment tool
 +
** Support for basic file attributes (permissions, owner, ...).
 +
** Support for multiple file-systems per archive.
 +
** Support for extended attributes (they are used by SELinux).
 +
** Support the basic file-system attributes (label, uuid, block-size) for all linux file-systems.
 +
** Support for [http://www.fsarchiver.org/Cloning-ntfs ntfs filesystems] (ability to create flexible clones of a Windows partitions).
 +
** Checksumming of everything which is written in the archive (headers, data blocks, whole files).
 +
** Ability to restore an archive which is corrupt (it will just skip the current file).
 +
** Multi-threaded lzo, gzip, bzip2, lzma compression.
 +
** Support for splitting large archives into several files with a fixed maximum size.
 +
** Encryption of the archive using a password. Based on blowfish from libcrypto from [[OpenSSL]].
 +
** Support backup of a mounted root filesystem (-A option).
 +
** Can be found on the [http://www.sysresccd.org/Main_Page System Rescue CD].
 +
|http://www.fsarchiver.org/Main_Page|{{Pkg|fsarchiver}}}}
 +
 
 +
* {{App|[[Wikipedia:Mondo Rescue|Mondo Rescue]]|A disaster recovery solution to create backup media that can be used to redeploy the damaged system.
 +
** Image-based backups, supporting Linux/Windows.
 +
** Compression rate is adjustable.
 +
** Can backup live systems (without having to halt it).
 +
** Can split image over many files.
 +
** Supports booting to a Live CD to perform a full restore.
 +
** Can backup/restore over NFS, from CDs, tape drives and and other media.
 +
** Can verify backups.
 +
|http://www.mondorescue.org/|{{AUR|mondo}}}}
 +
 
 +
* {{App|[[Partclone]]|A tool that can be used to back up and restore a partition while considering only used blocks.
 +
** Supports ''ext2'', ''ext3'', ''ext4'', ''hfs+'', ''reiserfs'', ''reiser4'', ''btrfs'', ''vmfs3'', ''vmfs5'', ''xfs'', ''jfs'', ''ufs'', ''ntfs'', ''fat(12/16/32)'', ''exfat''.
 +
** Supports compression.
 +
** Optionally, an ''ncurses'' interface can be used.
 +
|http://partclone.org/|{{Pkg|partclone}}}}
 +
 
 +
* {{App|PartedMagic|Live cd/usb with PartImage and other recovery tools.|3=http://partedmagic.com/doku.php?id=start|4=}}
 +
 
 +
* {{App|[[Wikipedia:Partimage|Partimage]]|An ''ncurses'' disk cloning utility for Linux/UNIX environments.
 +
** Has a Live CD.
 +
** Supports the most popular filesystems on Linux, Windows and Mac OS.
 +
** Compression.
 +
** Saving to multiple CDs or DVDs or across a network using Samba/NFS.
 +
|http://www.partimage.org/Main_Page|{{Pkg|partimage}}}}
 +
 
 +
* {{App|Q7Z|P7Zip GUI for Linux, which attempts to simplify data compression and backup.  It can create the following archive types: 7z, BZip2, Zip, GZip, Tar.
 +
** Updates existing archives quickly.
 +
** Backup multiple folders to a storage location.
 +
** Create or extract protected archives.
 +
** Lessen effort by using archiving profiles and lists.
 +
|http://k7z.sourceforge.net/|{{AUR|q7z}}}}
 +
 
 +
* {{App|[[Wikipedia:Redo Backup and Recovery|Redo Backup and Recovery]]|A backup and disaster recovery application that runs from a bootable Linux CD image.
 +
** Is capable of bare-metal backup and recovery of disk partitions.
 +
** Uses [http://www.xpud.org/ xPUD] and [[Partclone]] for the backend.
 +
|http://www.redobackup.org/|}}
 +
 
 +
* {{App|System Tar & Restore|Backup and Restore your system using tar or Transfer it with rsync
 +
** CLI and Dialog interfaces
 +
** Easy backup and restore wizards
 +
** Creates ''.tar.gz'', ''.tar.bz2'', ''.tar.xz'' or ''.tar'' archives
 +
** Supports openssl / gpg encryption
 +
** Uses rsync to transfer a running system
 +
** Supports Grub2, Syslinux, EFISTUB/efibootmgr and Systemd/bootctl
 +
|https://github.com/tritonas00/system-tar-and-restore|{{AUR|system-tar-and-restore}}}}
 +
 
 +
=== dd spin-offs ===
  
The basic procedure from a live environment will be:
+
Other ''dd''-like programs feature periodical status output, e.g. a simple progress bar.
* Create the new destination partition(s) using fdisk, cfdisk or other tools available in the live environment.
+
* Create a filesystem on each of the newly created partitions. Example:
+
mkfs -t ext3 /dev/sdb1
+
* Mount the source and destination partitions. Example:
+
mount -t ext3 /dev/sda1 /mnt/source
+
mount -t ext3 /dev/sdb1 /mnt/destination
+
* Copy the files from the source partition to the destination
+
cp -a /mnt/source/* /mnt/destination
+
'''-a''': preserve all attributes , never follow symbolic links and copy recursively
+
* Change the mount points of the newly cloned partitions in /etc/fstab accordingly
+
* Finally, install the GRUB bootloader if necessary. (See [[GRUB]])
+
  
==Disk cloning software==
+
; dcfldd : {{Pkg|dcfldd}} is an enhanced version of dd with features useful for forensics and security. It accepts most of dd's parameters and includes status output. The last stable version of dcfldd was released on December 19, 2006.<sup>[http://dcfldd.sourceforge.net/]</sup>
===Disk cloning in Arch===
+
The ncurses program [[wikipedia:Partimage|PartImage]] is in the community repos. The interface is not exceptionally intuitive but it works. There are currently no GTK/QT based disk cloners for Linux. Another option is to use dd, a small CLI image/file creation utility. The wikipedia has a list of various version of dd, specifically oriented to this purpose [[wikipedia:Dd_(Unix)#Recovery-oriented_variants_of_dd]]. [http://www.garloff.de/kurt/linux/ddrescue/ dd_rescue] works efficiently with corrupt disks copying error free areas first and later retrying error areas.
+
  
===Disk cloning outside of Arch===
+
; ddrescue : GNU {{Pkg|ddrescue}} is a data recovery tool. It is capable of ignoring read errors, which is a useless feature for disk wiping in almost any case. See the [http://www.gnu.org/software/ddrescue/manual/ddrescue_manual.html official manual] for details.
If you wish to backup or propagate your Arch install root, you are probably better off booting into something else and clone the partition from there. Some suggestions:
+
  
* [http://partedmagic.com/doku.php?id=start PartedMagic] has a very nice live cd/usb with PartImage and other recovery tools.
+
== See also ==
* [http://www.mondorescue.org/ Mindi] is a linux distribution specifically for disk clone backup. It comes with its own cloning program, Mondo Rescue.
+
* [[wikipedia:Acronis_True_Image|Acronis True Image]] is a commercial disk cloner for Windows. It allows you to create a live cd (from within Windows), so you do not need a working Windows install on the actual machine to use it.
+
* [http://www.fsarchiver.org/Main_Page FSArchiver] allows you to save the contents of a file system to a compressed archive file. Can be found on the [http://www.sysresccd.org/Main_Page System Rescue CD].
+
* [http://clonezilla.org/ Clonezilla] is an enhanced partition imager which can also restore entire disks as well as partitions.
+
* [http://redobackup.org/ Redo Backup and Recovery ] is a Live CD featuring a graphical front-end to partclone.
+
  
==External Links==
 
 
* [[Wikipedia:List of disk cloning software]]
 
* [[Wikipedia:List of disk cloning software]]
 
* [https://bbs.archlinux.org/viewtopic.php?id=4329 Arch Linux forum thread]
 
* [https://bbs.archlinux.org/viewtopic.php?id=4329 Arch Linux forum thread]

Latest revision as of 11:45, 14 May 2016

Disk cloning is the process of making an image of a partition or of an entire hard drive. This can be useful for copying the drive to other computers and for backup and recovery purposes.

Using dd

The dd command is a simple, yet versatile and powerful tool. It can be used to copy from source to destination, block-by-block, regardless of their filesystem types or operating systems. A convenient method is to use dd from a live environment, as in a Live CD.

Warning: As with any command of this type, you should be very cautious when using it; it can destroy data. Remember the order of input file (if=) and output file (of=) and do not reverse them! Always ensure that the destination drive or partition (of=) is of equal or greater size than the source (if=).

Tango-inaccurate.pngThe factual accuracy of this article or section is disputed.Tango-inaccurate.png

Reason: Are the conv= options safe to use? See: (Discuss in Talk:Disk cloning#remove conv sync noerror)

Cloning a partition

From physical disk /dev/sda, partition 1, to physical disk /dev/sdb, partition 1.

# dd if=/dev/sda1 of=/dev/sdb1 bs=64K conv=noerror,sync
Warning: If output file of= (sdb1 in the example) does not exist, dd will create a file with this name and will start filling up your root file system!

Cloning an entire hard disk

From physical disk /dev/sdX to physical disk /dev/sdY

# dd if=/dev/sdX of=/dev/sdY bs=64K conv=noerror,sync

This will clone the entire drive, including the MBR (and therefore bootloader), all partitions, UUIDs, and data.

  • noerror instructs dd to continue operation, ignoring all read errors. Default behavior for dd is to halt at any error.
  • sync fills input blocks with zeroes if there were any read errors, so data offsets stay in sync.
  • bs= sets the block size. Defaults to 512 bytes, which is the "classic" block size for hard drives since the early 1980s, but is not the most convenient. Use a bigger value, 64K or 128K. Also, please read the warning below, because there is more to this than just "block sizes" -it also influences how read errors propagate. See [1] and [2] for details and to figure out the best bs value for your use case.
Warning: The block size you specify influences how read errors are handled. Read below. For data recovery, use ddrescue.

The dd utility technically has an "input block size" (IBS) and an "output block size" (OBS). When you set bs, you effectively set both IBS and OBS. Normally, if your block size is, say, 1 MiB, dd will read 1024*1024 bytes and write as many bytes. But if a read error occurs, things will go wrong. Many people seem to think that dd will "fill up read errors with zeroes" if you use the noerror,sync options, but this is not what happens. dd will, according to documentation, fill up the OBS to IBS size after completing its read, which means adding zeroes at the end of the block. This means, for a disk, that effectively the whole 1 MiB would become messed up because of a single 512 byte read error in the beginning of the read: 12ERROR89 would become 128900000 instead of 120000089.

If you are positive that your disk does not contain any errors, you could proceed using a larger block size, which will increase the speed of your copying several fold. For example, changing bs from 512 to 64K changed copying speed from 35 MB/s to 120 MB/s on a simple Celeron 2.7 GHz system. But keep in mind that read errors on the source disk will end up as block errors on the destination disk, i.e. a single 512-byte read error will mess up the whole 64 KiB output block.

Tip: If you would like to view dd progressing, use the status=progress option. See dd for details.
Note:
  • To regain unique UUIDs of an ext2/3/4 filesystem, use tune2fs /dev/sdXY -U random on every partition.
  • Partition table changes from dd are not registered by the kernel. To notify of changes without rebooting, use a utility like partprobe (part of GNU Parted).

Backing up the MBR

The MBR is stored in the the first 512 bytes of the disk. It consist of 3 parts:

  1. The first 446 bytes contain the boot loader.
  2. The next 64 bytes contain the partition table (4 entries of 16 bytes each, one entry for each primary partition).
  3. The last 2 bytes contain an identifier

To save the MBR as mbr.img:

# dd if=/dev/sdX of=/path/to/mbr_file.img bs=512 count=1

To restore (be careful: this could destroy your existing partition table and with it access to all data on the disk):

# dd if=/path/to/mbr_file.img of=/dev/sdX

If you only want to restore the boot loader, but not the primary partition table entries, just restore the first 446 bytes of the MBR:

# dd if=/path/to/mbr_file.img of=/dev/sdX bs=446 count=1

To restore only the partition table, one must use:

# dd if=/path/to/mbr_file.img of=/dev/sdX bs=1 skip=446 count=64

You can also get the MBR from a full dd disk image:

# dd if=/path/to/disk.img of=/path/to/mbr_file.img bs=512 count=1

Create disk image

1. Boot from a live media.

2. Make sure no partitions are mounted from the source hard drive.

3. Mount the external HD

4. Backup the drive.

# dd if=/dev/sdX conv=sync,noerror bs=64K | gzip -c  > /path/to/backup.img.gz

If necessary (e.g. when the format of the external HD is FAT32) split the disk image in volumes (see also the split man pages).

# dd if=/dev/sdX conv=sync,noerror bs=64K | gzip -c | split -a3 -b2G - /path/to/backup.img.gz

If there is not enough disk space locally, you may send the image through ssh:

# dd if=/dev/sdX conv=sync,noerror bs=64K | gzip -c | ssh user@local dd of=backup.img.gz

5. Save extra information about the drive geometry necessary in order to interpret the partition table stored within the image. The most important of which is the cylinder size.

# fdisk -l /dev/sdX > /path/to/list_fdisk.info
Note: You may wish to use a block size (bs=) that is equal to the amount of cache on the HD you are backing up. For example, bs=8192K works for an 8 MiB cache. The 64 KiB mentioned in this article is better than the default bs=512 bytes, but it will run faster with a larger bs=.

Restore system

To restore your system:

# gunzip -c /path/to/backup.img.gz | dd of=/dev/sdX

When the image has been split, use the following instead:

# cat /path/to/backup.img.gz* | gunzip -c | dd of=/dev/sdX

Using ddrescue

ddrescue is a tool designed for cloning and recovering data. It copies data from one file or block device (hard disc, cdrom, etc) to another, trying to rescue the good parts first in case of read errors, to maximize the recovered data.

To clone a faulty or dying drive, run ddrescue twice. First round, copy every block without read error and log the errors to rescue.log.

# ddrescue -f -n /dev/sdX /dev/sdY rescue.log

Second round, copy only the bad blocks and try 3 times to read from the source before giving up.

# ddrescue -d -f -r3 /dev/sdX /dev/sdY rescue.log

Now you can check the file system for corruption and mount the new drive.

# fsck -f /dev/sdY

Disk cloning software

These applications allow easy backup of entire filesystems and recovery in case of failure, usually in the form of a Live CD or USB drive. They contain complete system images from one or more specific points in time and are frequently used to record known good configurations.

See also Synchronization and backup programs for other applications that can take full system snapshots, among other functionality.

  • Acronis True Image — Commercial disk cloner for Windows. It allows you to create a live (from within Windows), so you do not need a working Windows install on the actual machine to use it. After registration of the Acronis software on their website, you will be able to download a Linux-based Live CD and/or plugins for BartPE for creation of the Windows-based live CD. It can also create a WinPE Live CD based on Windows. The created ISO Live CD image by Acronis doesn't have the hybrid boot ability and cannot be written to USB storage as a raw file.
http://www.acronis.com/products/trueimage/ ||
  • Arch Backup — A trivial backup script with simple configuration.
    • Configurable compression method.
    • Multiple backup targets.
http://code.google.com/p/archlinux-stuff/ || arch-backupAUR
  • Clonezilla — A disaster recovery, disk cloning, disk imaging and deployment solution.
    • Boots from live CD, USB flash drive, or PXE server.
    • Supports ext2, ext3, ext4, reiserfs, reiser4, xfs, jfs, btrfs FAT32, NTFS, HFS+ and others.
    • Uses Partclone (default), Partimage (optional), ntfsclone (optional), or dd to image or clone a partition.
    • Multicasting server to restore to many machines at once.
    • Included on the Arch Linux installation media.
http://clonezilla.org/ || clonezilla
  • FSArchiver — A safe and flexible file-system backup and deployment tool
    • Support for basic file attributes (permissions, owner, ...).
    • Support for multiple file-systems per archive.
    • Support for extended attributes (they are used by SELinux).
    • Support the basic file-system attributes (label, uuid, block-size) for all linux file-systems.
    • Support for ntfs filesystems (ability to create flexible clones of a Windows partitions).
    • Checksumming of everything which is written in the archive (headers, data blocks, whole files).
    • Ability to restore an archive which is corrupt (it will just skip the current file).
    • Multi-threaded lzo, gzip, bzip2, lzma compression.
    • Support for splitting large archives into several files with a fixed maximum size.
    • Encryption of the archive using a password. Based on blowfish from libcrypto from OpenSSL.
    • Support backup of a mounted root filesystem (-A option).
    • Can be found on the System Rescue CD.
http://www.fsarchiver.org/Main_Page || fsarchiver
  • Mondo Rescue — A disaster recovery solution to create backup media that can be used to redeploy the damaged system.
    • Image-based backups, supporting Linux/Windows.
    • Compression rate is adjustable.
    • Can backup live systems (without having to halt it).
    • Can split image over many files.
    • Supports booting to a Live CD to perform a full restore.
    • Can backup/restore over NFS, from CDs, tape drives and and other media.
    • Can verify backups.
http://www.mondorescue.org/ || mondoAUR
  • Partclone — A tool that can be used to back up and restore a partition while considering only used blocks.
    • Supports ext2, ext3, ext4, hfs+, reiserfs, reiser4, btrfs, vmfs3, vmfs5, xfs, jfs, ufs, ntfs, fat(12/16/32), exfat.
    • Supports compression.
    • Optionally, an ncurses interface can be used.
http://partclone.org/ || partclone
  • PartedMagic — Live cd/usb with PartImage and other recovery tools.
http://partedmagic.com/doku.php?id=start ||
  • Partimage — An ncurses disk cloning utility for Linux/UNIX environments.
    • Has a Live CD.
    • Supports the most popular filesystems on Linux, Windows and Mac OS.
    • Compression.
    • Saving to multiple CDs or DVDs or across a network using Samba/NFS.
http://www.partimage.org/Main_Page || partimage
  • Q7Z — P7Zip GUI for Linux, which attempts to simplify data compression and backup. It can create the following archive types: 7z, BZip2, Zip, GZip, Tar.
    • Updates existing archives quickly.
    • Backup multiple folders to a storage location.
    • Create or extract protected archives.
    • Lessen effort by using archiving profiles and lists.
http://k7z.sourceforge.net/ || q7zAUR
  • Redo Backup and Recovery — A backup and disaster recovery application that runs from a bootable Linux CD image.
    • Is capable of bare-metal backup and recovery of disk partitions.
    • Uses xPUD and Partclone for the backend.
http://www.redobackup.org/ ||
  • System Tar & Restore — Backup and Restore your system using tar or Transfer it with rsync
    • CLI and Dialog interfaces
    • Easy backup and restore wizards
    • Creates .tar.gz, .tar.bz2, .tar.xz or .tar archives
    • Supports openssl / gpg encryption
    • Uses rsync to transfer a running system
    • Supports Grub2, Syslinux, EFISTUB/efibootmgr and Systemd/bootctl
https://github.com/tritonas00/system-tar-and-restore || system-tar-and-restoreAUR

dd spin-offs

Other dd-like programs feature periodical status output, e.g. a simple progress bar.

dcfldd 
dcfldd is an enhanced version of dd with features useful for forensics and security. It accepts most of dd's parameters and includes status output. The last stable version of dcfldd was released on December 19, 2006.[3]
ddrescue 
GNU ddrescue is a data recovery tool. It is capable of ignoring read errors, which is a useless feature for disk wiping in almost any case. See the official manual for details.

See also