Cloning a hard drive
In one of my computers, I have one hard drive that contains 2 partitions: 1 for the root filesystem and one for my /home partition. When I bought a new hard drive, I needed to clone the old one on the new one. This can be easily done with "dd" as long as your partitions are the same size. So I decided to keep the root filesystem with the same size, but wanted to grow the /home partition.
Create the partitions
First, you need to create the partitions on the new drive using fdisk. Remember to keep the same size for the partitions you wanna clone. If you create them smaller, you will end up with a corrupted filesystem. If you create them larger, you will not be able to access the extra space so it will be wasted. After creating the partitions, you don't need to create a filesystem on them (mkfs) since "dd" will clone the partition table of the old hard drive too. But of course, you will need to create a FS for the other partitions that won't be cloned.
You need to clone your master boot record (which contains lilo/grub). We need to copy the first 512 bytes (the first sector):
dd if=/dev/sda of=/dev/sdb bs=512 count=1
Then, we can clone the partition:
dd if=/dev/sda1 of=/dev/sdb1 bs=4096 conv=noerror
At this point, my root partition was cloned successfully. For the other partition (/dev/sdb2), I had to create a new filesystem (mkfs) because my partition needed to be larger. After that, I copied the files manually using "cp".