I have a 15" unibody MacBook Pro, 2.4 GHz processor and 2 GB RAM, running OS X 10.5.6. The laptop has a 250 GB disk on board, standard equipment. I have been using Time Machine to back up to a 1 TB external (USB) hard disk, and the back up drive now contains 271 GB of stuff. I wanted to clone the backup drive onto a new drive, and then alternately back up to one or the other and keep one off-site. I got a second 1 TB drive, but partitioned it into 250 GB and 731 GB. I then attempted to clone the 271 GB of backup from the old backup drive into the 731 GB partition of the new drive. It simply will not work. Carbon Copy Cloner froze three times while attempting to copy. It never gave any reason, or any error message, it would just completely freeze and not make a single byte of progress for an hour. SuperDuper! made continuous progress for 5 hours 21 minutes, copying "221 GB", but then passed an error "file or directory does not exist". I don't know how to interpret the 221 GB, because there is 271 GB of used space on the source drive, but the progress bar made it look as if it was copying all 932 GB of capacity. Do the two drives need to be exactly and precisely the same size? The documentation for both cloning utilities says no. Do I have to make sure Time Machine is completely turned off? Well, I did, and it still failed. Also, how can these utilities clone the boot drive while the OS is running if they can't handle a little simultaneous activity? Please help, thanks.