# 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. There is also a dedicated page File Recovery.

## 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 (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=).

### 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,sync

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

From physical disk /dev/sda to physical disk /dev/sdb

    dd if=/dev/sda of=/dev/sdb bs=4096 conv=notrunc,noerror,sync

This will clone the entire drive, including MBR (and therefore bootloader), all partitions, UUIDs, 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 read errors. Default behavior for dd is to halt at any error.
- sync writes zeroes for read errors, so data offsets stay in sync.
- bs=4096 sets the block size to 4k, an optimal size for hard disk read/write efficiency and therefore, cloning speed.

Note: To regain unique UUIDs, use "tune2fs /dev/sdbX -U random" on every partitions.
Note: Partition table changes from dd are not be 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 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

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

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=.

### Restore system

To restore your system:

     # gunzip -c /mnt/sda1/hda.img.gz | dd of=/dev/hda

### 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.

#### 7zip

Install the p7zip package from the official repositories. This backup example will split the dd command output in the files by up to the 100 megabyte each:

    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

Note: 7zip can split only the 7z compression type files

#### Zip

Install the zip package from 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. Backup:

    dd if=/dev/sdXY | zip --compression-method bzip2  image-file.zip -

Restore:

    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.

See also `man zip` for more information.

#### Rar

Install the rar package from the AUR.

Warning: The rar examples were made based on the manuals, please confirm!

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 unrar utility. The unrar utility is available in the official repositories and can be installed with `pacman -S unrar`.

#### Bzip2

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

or

    $ bzcat compressedfile.bzip2 | dd of=/dev/sdXY

Warning: Never ever use the `bzip2 -kdc imgage.bzip2 > /dev/sdXY` and `bzip2 -kc /dev/sdXY > imgage.bzip2` methods 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.

## 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.

Note: This method should not be considered in the same category as disk cloning on the level at which dd operates. Also, it has been reported that even with the -a flag, some extended attributes may not be copied. For better results, rsync or tar should be used.

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 cd (from within Windows), so you do not need a working Windows install on the actual machine to use it.
- 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.
- Redo Backup and Recovery is a Live CD featuring a graphical front-end to partclone.

## External Links

- Wikipedia:List of disk cloning software
- Arch Linux forum thread

Categories:

- Data compression and archiving
- System recovery