Answer by psusi for How can I use DD to migrate data from an old drive to a new drive?

While you can use dd to copy a disk like that, doing so has a number of drawbacks:

1. The destination must be exactly the same size or larger than the source
2. After copying, you will need to resize the partitions to use any additional space
3. You will waste time copying free space
4. Any fragmentation present in the old disk is preserved

Using an imaging program like Ghost4Linux, partclone, or clonezilla at least takes care of numbers 2 and 3. You can also simply format the new disk, mount it, and copy all of the files over with cp -ax ( as root ), and then reinstall the boot loader on the new drive. This method does not suffer from any of the above drawbacks.