zh-cn:Disk cloning Disk cloning is the process of making an image of a partition or an entire hard drive. This can be useful for copying the drive to other computers and for backup and recovery purposes.
- 1 Using dd
- 2 Using cp
- 3 Disk cloning software
- 4 External Links
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.
- This paragraph used to contain several errors that misrepresented the inner workings of the dd command. I tried to fix them, but YMMV.
- 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 (
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=512 conv=noerror,sync
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/sda to physical disk /dev/sdb
# dd if=/dev/sda of=/dev/sdb bs=512 conv=noerror,sync
This will clone the entire drive, including MBR (and therefore bootloader), all partitions, UUIDs, and data.
noerrorinstructs dd to continue operation, ignoring all read errors. Default behavior for dd is to halt at any error.
syncfills input blocks with zeroes if there were any read errors, so data offsets stay in sync.
bs=512sets the block size to 512 bytes, the "classic" block size for hard drives. If and only if your hard drives have a 4K block size, you may use "4096" instead of "512". Also, please read the warning below, because there is more to this than just "block sizes" - it also influences how read errors propagate.
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, 1M, dd will read 1M bytes and write 1M 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, which means adding zeroes at the end of the block. This means, for a disk, that effectively the whole 1M would become messed up because of a single 512 byte read error in the beginning of the read: ERROR6789 would become 678900000 instead of 000006789.
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 manyfold. For example, changing bs from 512 to 64K changed copying speed from 35MB/s to 120MB/s on a simple Celeron 2.7GHz 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 bytes read error will mess up the whole 64k output block.
pidof ddwill tell you the PID of dd, then use
kill -USR1. In one line:
kill -USR1 $(pidof dd).
- To regain unique UUIDs, use "tune2fs /dev/sdbX -U random" on every partitions. (works for ext* file systems only)
- 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 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":
# dd if=/dev/hda of=/mnt/sda1/mbr.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=/mnt/sda1/mbr.img of=/dev/hda
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
To restore only the partition table, one must use
# dd if=/mnt/sda1/mbr.img of=/dev/hda 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=/mnt/sda1/mbr.img bs=512 count=1
Create disk image
1. Boot from a liveCD or liveUSB.
2. Make sure no partitions are mounted from the source hard drive.
3. Mount the external HD
4. Backup the drive.
# dd if=/dev/hda conv=sync,noerror bs=64K | gzip -c > /mnt/sda1/hda.img.gz
If necessary (e.g. when the format of the external HD is FAT32) split the disk image in volumes (see also split man pages).
# dd if=/dev/hda conv=sync,noerror bs=64K | gzip -c | split -a3 -v2G - /mnt/sda1/hda.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/hda > /mnt/sda1/hda_fdisk.info
To restore your system:
# gunzip -c /mnt/sda1/hda.img.gz | dd of=/dev/hda
# cat /mnt/sda1/hda.img.gz* | gunzip -c | dd of=/dev/hda
when the image has been split in volumes.
Examples with compression
When you need to create the hard drive or a single partition compressed backup image file you must use compression tools which can do backup from a stdout and the dd command. Those compressed files cannot be mounted by the mount command but are useful to know how to create and restore them.
Install the official repositories. This backup example will split the dd command output in the files by up to the 100 megabyte each:package from the
dd if=/dev/sdXY | 7z a -v100m -t7z -si image-file.7z
Restore with 7zip:
7z x -so image-file.7z | dd of=/dev/sdXY
Install the official repositories, which contains zipsplit among other utilities for the management of zip archives.
It will create a file with "-" name inside the image-file.zip file which will contain data from the dd command output. To make a raw output of the file you can use the
-cp option with unzip in stdout for the dd command.
dd if=/dev/sdXY | zip --compression-method bzip2 image-file.zip -
unzip -cp image-file.zip | dd of=/dev/sdXY
The zip tool cannot split files on the fly but you can use the
zipsplit utility on an already created file.
man zip for more information.
Install the AUR.AUR package from the
This should do a backup and split the creating file on the fly in by up to 150 megabyte files each.
dd if=/dev/sdXY | rar a -v150m -siimage-file.rar
This should restore
unrar x -p image-file.rar | dd of=/dev/sdXY
or you can use the rar instead of the
pacman -S unrar.
Creation by using the dd is more safe and use to be error free:
dd if=/dev/sdXY | bzip2 -f5 > compressedfile.bzip2
937016+0 records in 937016+0 records out 479752192 bytes (480 MB) copied, 94.7002 s, 5.1 MB/s
And a safe way of restoring with combination of the dd:
$ bunzip2 -dc compressedfile.bzip2 | dd of=/dev/sdXY
$ bzcat compressedfile.bzip2 | dd of=/dev/sdXY
bzip2 -kdc imgage.bzip2 > /dev/sdXYand
bzip2 -kc /dev/sdXY > imgage.bzip2methods for serious backup of partitions and disks. The errors might be due the end of the device or partition and the restore process gives also errors due the truncated end.
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.
The basic procedure from a live environment will be:
- 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
Disk cloning in Arch
- Partclone provides utilities to save and restore used blocks on a partition and supports ext2, ext3, ext4, hfs+, reiserfs, reiser4, btrfs, vmfs3, vmfs5, xfs, jfs, ufs, ntfs, fat(12/16/32) and exfat. Optionally, a ncurses interface can be used. Partclone is available in the community repository.
- Partimage, an ncurses program, is available in the community repos. Partimage does not currently support ext4 or btrfs filesystems. NTFS is experimental.
Disk cloning outside of Arch
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:
- PartedMagic has a very nice live cd/usb with PartImage and other recovery tools.
- Mindi is a linux distribution specifically for disk clone backup. It comes with its own cloning program, Mondo Rescue.
- Acronis True Image is a 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 regitratinon 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.
- FSArchiver allows you to save the contents of a file system to a compressed archive file. Can be found on the System Rescue CD.
- Clonezilla is an enhanced partition imager which can also restore entire disks as well as partitions. Clonezilla is included on the Arch Linux installation media.
- Redo Backup and Recovery is a Live CD featuring a graphical front-end to partclone.