Help!!! Lost all data on internal & FireWire drives

I've never heard of anything remotely like what you describe, and I can't think of any way it could happen. Do you have any other backups? If not, I think you should take your malfunctioning Mac and your external drive to an Apple Store, rather than trying to solve this problem yourself.

As strange as it sounds, there have been a number of others who have recently reported similar disasters associated with a failed XCode install - see these threads:

*All mounted volumes erased when system crashed during XCode install*
http://discussions.apple.com/thread.jspa?messageID=13282009

*Install Xcode from the App Store = Deleted System*
http://discussions.apple.com/thread.jspa?messageID=13226070

Unbelievable. That's class-action material.

It seems that you may be the victim of the worst software bug I've ever heard of, on any platform. If your only backup drive has been erased, it's all the more important that you take the problem directly to Apple without doing anything else yourself. If Apple is responsible for your loss, it should do whatever is necessary to restore your data, even if that means paying for your drives to be processed by a data recovery service.

It sounds just awful 😟 . We all wish you the very best of luck in in your recovery efforts.

Please do contact Apple immediately and refer them to these threads to be sure they are aware of this issue - I have never heard of a previous bug with such catastrophic consequences.

Not as nasty, but a failed XCode 4 install rendered by boot drive unbootable. I did not loose data on any other of the 4 internal and 2 external drives that were attached at the time, including the boot drive. The install for the latest XCode that supports iOS 4.3.1 stalled about 2/3 the way while it was moving files. I did a hard reboot after 20 minutes without progress. I get as far as the Apple logo and spinning indicator, but cannot complete booting, even in safe mode. I can access everything on the corrupt boot drive including fixing permissions and checking the disk, but still cannot boot to it even though it is listed as a boot option. I now am backing up the data from the corrupt drive and will restore the drive from a somewhat outdated backup boot drive.