Hard drive filled up after I did back up using Superduper

Question

I bought a new Macbook Air. I was going to back up my old Macbook Air data onto an external drive before I set up the new Macbook Air. Also my old Macbook Air (1.86 GHz, 120GB HDD) had a broken hinge and I was going to take it to the Apple A/S center to have the hinge repaired. So I wanted to back up my data just in case.
I have backed up the data from the old Macbook Air using the same external drive twice before using Superduper and it seemed to go fine both occasions. I have OS 10.6.0 on the old Macbook Air.
I am typing this on the new Macbook Air by the way (2.16GHz, 256 GB, 4GB memory).
I use the unregistered version of the Superduper that requires you to erase and then do a full backup.
I plugged in the external drive using a powered USB hub. (On previous occasions I have used a USB cord that plugs into two computers, as one computer doesn't provide enough power; this time I forgot to set up the second computer and just plugged it into the hub. The blue light came up on the external drive when I plugged it in.)
It came up with "Untitled", an orange icon, on the Superduper window. It asked me whether I want to copy Macintosh HD to "Untitled". I pressed "OK".
It started copying.
Then I was doing something nearby the computer and accidentally tugged on the lid of the Macbook Air. The hinge is broken and as soon as I touched the Macbook Air lid, the lid laid flat on the table, with the laptop completely open. It does that occasionally because the hinge is broken and the slightest pressure on the lid means it will spring right open (180 degrees).
I checked the Superduper window and it seemed to be copying OK. The number of files copied was going up and up.
However I got a message that said that I hadn't ejected the disk properly and that could damage the disk.
I assumed that meant the external drive "Untitled". I thought I should end the copying and start again.
So I quit Superduper. Something strange happened after that. I can't remember what it was exactly. I think it didn't want to quit. I had to use Force Quit.
I then unplugged and plugged the external drive back into the hub. I opened Superduper. This time it had "Untitled 2".
I thought that was strange, and I restarted the computer hoping to see "Untitled" in the Superduper after restarting the computer and opening Superduper again.
However, I got "Untitled 2" again even though the icon of the external hard drive was labeled "Untitled" on my Desktop.
(I think this is where I went wrong.)
I pressed copy again. About halfway through it suddenly stopped and said that the copying had failed.
I unplugged the external hard drive and plugged it in again, and restarted the computer. I opened Superduper again and this time I could not get it to copy. The copy part was grayed out.
I opened Disk Utility and checked the "Untitled" disk. It said it was fine. Verify was OK.
But when I checked the Macintosh HD I got all these error messages and the volume was full. 105GB was used up and 0 GB was available.
Very strange as I had about 20GB available before I tried to do the backup. (I checked the disk capacity of the HD before I did the backup.) I knew for sure that my hard drive was not full before I did the backup.
I tried to repair it but it didn't work. It told me to restart using the operating disk and use First Aid.
I put in the Snow Leopard operating disk in the Superdrive and restarted the computer holding down "C".
The operating disk came up, I chose English and chose Disk Utility. I tried repair. It gave messages that the Library Core had been changed. It said the disk was repaired and OK now. However, the volume was still 105 GB with about 12MB available (before I did the Disk Utility using the OS disc, I deleted a few music files.)
I just restarted the computer after having removed the Superdrive from the computer and it took like twenty minutes to restart. It has restarted though finally (while I am typing this).
I don't know what to do. I don't know what I did to corrupt the disk. I do not want to make things worse. So far the Desktop looks unchanged.
I can't do anything because it seems the computer's hard drive is full eg. browse the internet properly – it keeps coming up with error messages about Preferences being changed.
I think the disk got full because I inadvertently was backing up onto the computer's hard drive (the 'Untitled 2' was probably somewhere on the hard drive of the computer, and not the external hard drive.
I am worried that I have wrecked the back up drive and I have ruined the MBA's hard drive.
What should I do?
Should I just delete some files including program files and free up some space at least 2 GB? I can delete heavy duty program files like Adobe Creative Suite from Applications. (I have the disks so I can always reinstall them again.) What about deleting MS Office? (I have the disk for that.) Will doing that affect the Photoshop files and the Word files I already have?
What do you recommend I delete so that I can free up lots of space?
And how do I find what is filling up my laptop and why there is almost zero GB left on my hard drive. If I did do a backup onto the hard drive where do I find this and how can I delete it?
I was planning to do the backup and on the new MBA do a migration of everything on the backup using the Superdrive – a clone. I have done this before (when I bought the old MBA) and it worked (I did clean install a few times when I mucked up the hard drive in the past and restored the clone that was on the backup external drive onto the computer).
How can I tell if the external drive that I tried backing up onto is OK?
I thought I would check here before I did anything in case I made things worse.
I am going to use the latest operating system on the new Macbook Air. I have read here that 10.6.0 is risky – all your data can suddenly be erased.
I will also update the old Macbook Air to 10.6.4 once I have got things fixed on it.
Thanks for any advice.

Answer 1

There may be one or more large folders in your /Volumes folder that shouldn't be there and are using up your disk space.
/Volumes is an 'invisible" folder at the root level of your internal drive which is supposed to contain only the "mount points" for your attached disk volumes, but sometimes an actual folder can mistakenly get created there, often as a result of a failed copy operation such as you experienced with SuperDuper. Such a "ghost" folder will have a name similar to a real external drive, and can contain data that was meant for the real external drive but never got there. When the real external volume then re-mounts, it can no longer use its own name for the mount point in /Volumes because that name is already "taken", and so an extra number gets appended to the mount point. This may have happened twice in your situation, since the actual drive is now mounting as "Untitled 2".
/Volumes is a hidden folder, but it's easy to peek into it. First you should *eject and then physically disconnect all external drives*. Then:
Finder>Go menu> Go to Folder
enter /Volumes and click Go
You should see an alias to the startup volume. Don't touch this, or any other aliases. Do you also see a large folder named "Untitled, and perhaps another folder named "Untitled 1," which are not aliases? If so, delete them, and restart.