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I made a horrible mistake: I ran dd on an external hard drive, that was the Time Machine backup storage, to make it bootable. After a few seconds I cancelled the command, but the hard drive is shaped as bootable image, and the backup folder is missing.
What can I do?
Sounds like you started to overwrite the drive. The data is probably still recoverable, but, as Graham said, you don't want to do anything to the drive until you attempt to recover the files.
A few options:
While I haven't used it, PhotoRec looks like a good option, if you are comfortable with the command line. Despite the name, it can recover all sorts of file types. It only reads the disk, so your data should be safe even if it is unable to recover it.
For a graphical (and more expensive option), Disk Drill has gotten good reviews. It's pricey at $89, but you can use a free version to preview what it would be able to recover.
If you're in the market for a general disk protection utility, Tech Tool Pro 7 has a data recovery mode. Also, you can set it up to monitor your drives going forward, which would protect against future errors.
DrDD won't completely solve your problem, but it is a graphical way of copying the raw data off your Time Machine drive. I'm not 100% sure that the above programs will be able to read from the copy, but if they can, it would give you another margin of safety. It's also designed to protect your data on failing hard drives, so it should be safe to use in your case.
Hope this helps.
I'm a big fan of Data Rescue for data recovery. If you have a little money to spend, it's one of the best tools for the job.
If you have a little more money to spend, Drive Savers may be able to help.
Recovering a few files (or even most of them) in a backup does you no good. It's no longer a backup. I wouldn't even attempt to recover from this problem. Wipe the drive, let TM start backing up anew to it, and chalk this up as a lesson learned.
It's easy to keep Time Machine itself backed up. Just start a TM backup on a different disk, and occasionally swap the drives. The initial backup will still take a long time, but when you rotate back in a previous TM backup, TM only needs to copy what's new for that drive. If you can keep them both attached, TM will even do the rotation for you.
I started doing that (keeping multiple TM backups) after losing a TM drive to hardware failure. Then I discovered it's really convenient for off-site backup. TM can bring a backup disk up to date much faster than the other backup solutions (SuperDuper, CarbonCopyCloner) can.
