Upgrade time machine storage? I'm going to buy 2T external HDD to replace my already full 1T HDD external. I want to keep the time machine backup data. In this case, is it just OK to copy all the time machine backup data in 1T HDD to 2T HDD?
I know this might be old, but here are the right steps to perform a Time Machine hard drive replacement preserving old backups, without having to use CCC or SuperDuper! (which I love, but are not needed). 

I have a Mac Pro so to make things more complicated I added Two drives and created a RAID-1 (Mirror); once the mirror was working, I proceeded with these steps (sans the “plug drive”) ;)

The above comment is to demonstrate that the volume composition doesn’t affect this. 

Like with any other Hard Drive operation, always make sure you have a backup or a way to restore your information in case something goes wrong. Read before you click “ok”. Use common sense and be careful. 

You need to be familiar with Disk Utility (located in /Applications/Utilities/Disk Utility.app). It’s a very simple and straightforward application, but also very dangerous if you go coo coo and start clicking things without reading.

TIME MACHINE HARD DRIVE MIGRATION TO A NEW DRIVE PRESERVING BACKUP HISTORY


Plug your new (presumably bigger) drive. Using Disk Utility, create the HFS+ Journaled partition (make sure you use GUID to avoid problems). Give it a name like: NewTM (you can change that later). (This may be obvious but if you have a Mac Pro, turn it off before inserting the drives…) 
Open the Time Machine configuration and turn off Time Machine. 
Unmount the Time Machine drive (the ‘old’) and mount it again. This causes the drive to be mounted as a regular drive and not have the “Time Machine” Green Icon. (This is important). You can do that from Disk Utility. 
Now go back to Disk Utility (/Applications/Utilities/Disk Utility.app) and click on the restore tab. 
You will see two boxes to type, but you can also drag and drop, so drag the “TimeMachine” (old) to the source box (the upper one).
Drag the new “NewTM” partition to the target box (lower one). 
IMPORTANT: select “Erase Destination” so there’s a block level copy.
Click restore and make sure that you have the right partitions (i.e.: read what you are being shown in the popup, it’s your last chance or you could erase your data.) When you’re satisfied, click ok to the popup and go cook. My 750gb took over four hours (and it was a SATA drive). Consider that USB drives (and even Firewire 800) are slower than any SATA internal drive. Some people reports this to take over five hours over USB for much smaller drives, so be patient.
Here’s how mine looked:




If everything went right, you should see two identical drives on your desktop, that is because the old drive was “fully duplicated” in the new one. The difference should be the free space, the new one should have more (if you are using a larger drive of course).

We’re almost done, but we need to activate Time Machine again. 


Unmount the old Time Machine drive. If you are unsure which one it is, check the free space and/or physically disconnect it; don’t worry, you’ll be able to use it again soon.
Open the TimeMachine configuration screen again and press Change Drive. Select the new one (should be the only one called Time Machine). The disk should now turn “green” with the Time Machine icon. Congratulations, you’ve migrated your Time Machine. 


What now?

Test it. Use Time machine to see if your files are there, recover some old files to see if they come, make sure everything is ok, you can reconnect your old drive and format it, or use it for furniture if you want. 

If you previously had Spotlight configured to exclude your Time Machine, you might want to make sure that everything is ok. Maybe you’ll have to drag the Time Machine drive again. Just check it. 

And that’s all. I hope you don’t destroy your data in the process. I came up with these steps by googling, experimenting and using common sense :) Hope it helps.