Help! Yosemite install Failed, TM won't recover

[jeepstylexx]

Attempted to update my OS to Yosemite using the app store update. Everything appeared to be fine until I got a stuck black status bar and spinning wheel for hours. I rebooted and now get a black screen with spinning multi color wheel. I used the recovery setting to attempt to use time machine to restore and I'm getting a message that my TM backup can't be used as it's corrupt!!!

I CAN'T lose the data on the drive. I tried to reinstall the OS using the internet through recovery but I get the following message:

"An additional 686 mb of space is needed to install on this disk. Try removing items from the disk to make space."

How do I remove items if the MacBook air won't boot???? What options do I have to save the data on the current drive. Would a disk image copy work?

Thanks!

 

[sosull]

Not that I've ever experienced the problem myself, but I'd assume you would use another Mac connected to your MacBook Air via Thunderbolt. Boot into Target Disk Mode, retrieve the user folder to an external hard disk (don't forget to back up important elements of the library folder like fonts). Make up a bootable Yosemite USB stick, and use it to install a clean OS on the MacBook Air.

 

[jeepstylexx]

this is the only computer I own. I don't have another mac to connect it to. Do u know if the disk image backup will work?

 

[sosull]

In principle it should work yes. If you can access disk utility via Internet recovery and make a disk image clone from there, then you might not need to use target disk mode. Instead, you'd make the clone and boot from the external disk (by holding option while you turn the MacBook on).

Make sure that you have a way of checking that your backed up files are present and in working order. The main priority isn't convenience – it's preventing a catastrophic data loss.