Clone existing EXT to new EXT drive

Hi all,
I have searched and found the answer to my problem but I am intrigued about one thing.
I had an existing external drive for TM backups. I wanted to replace this with a larger cpacity external drive. I wanted to clone all the existing TM backups from the old drive to the new one and then use the new drive for all future backups.
Many posts said that the disc utility within OS X could do this, but it continually failed. I solved it by using super duper.
But why would disc utility fail?
Just interested if anyone else has experienced this, or what could possibly be wrong.
Thanks
Neil

I believe both SuperDuper and Carbon Copy Cloner use a sector by sector copy method which results in true cloning whereas Disk Utility will only make an image. I don't think you did anything wrong. In any event, SuperDuper or CCC are the proper utilities to use - which you found out. ;D

Regards.