All you want to know about DD

DD

Here's a quick list of cool examples for the dd tool:

Create a backup
dd if=/dev/sda of=/opt/backup_sda.img

Restore a backup
dd if=/opt/backup_sda.img of=/dev/sda

Clone a hard disk
dd if=/dev/sdb of=/dev/sdc

Transfer a disk image
dd if=/dev/sdb | ssh root@target "(cat >backup.img)"

Create an iso image of a CD/DVD
dd if=/dev/cdrom of=cdimage.iso

Burn an iso image of a CD/DVD
dd if=cdimage.iso of=/dev/cdrom obs=32k seek=0

Rescue a file that contains bad blocks
dd if=movie.avi of=rescued_movie.avi conv=noerror

Create your own bootloader
dd conv=notrunc if=bootloader of=qemu.img

Create a backup of your MBR
dd if=/dev/sdb of=mbr_backup bs=512 count=1

Restore a backup of your MBR
dd if=mbr_backup of=/dev/sdb bs=512 count=1

Mount dd image of and entire disk
You must use the start number of the partition.
fdisk -u -l disk_image
Disk /mnt/storage/disk_image: 0 MB, 0 bytes 255 heads, 63 sectors/track, 0 cylinders, total 0 sectors Units = sectors of 1 * 512 = 512 bytes Disk identifier: 0x41172ba5
                  Device Boot      Start         End      Blocks   Id  System /mnt/storage/disk_image1              63       64259       32098+  de  Dell Utility /mnt/storage/disk_image2   *       64260    78108029    39021885    7  HPFS/NTFS Partition 2 has different physical/logical endings:phys=(1023, 254, 63) logical=(4861, 254, 63)
Then take the start of the partition that you want to edit 64260 in this case and multiply it by 512 ie 512*64260=32901120
mount -o loop,offset=32901120 -t auto /mnt/storage/disk_image /mnt/drive_image

When the hard disk has errors
Get the dd_rescue tool
dd_rescue /dev/sdb /opt/backup_sdb.img

Network Clone
Destination: nc -l -p 2222 | dd of=/dev/sda bs=16M
Origin: dd if=/dev/sda bs=16M | nc $Destination 2222

Network speed test 
dd if=/dev/zero bs=1M count=100 | ssh user@machine 'cat > /dev/null'