How to restore a Time Machine backup from a 2 HDD setup to a single HDD
After a lot of searching and messing around I found the answer.... thanks to this post

/System/Library/Extensions/TMSafetyNet.kext/Contents/Helpers/bypass will allow you to make changes.

BUT....  I could not perform a mv so I resorted to using rsync right on the TM backup and ignored most of all my files.  This in turn allowed me to restore to a slimmed down backup.

After this I tried using Time Machine to copy the rest of my files back to my home folder, it kept failing.

In the end, enabling guest login and using rsync got me what I wanted.

If I had to do this again I would do it this way;


Do the restore as per normal, the login WILL FAIL! this is because
your home folder is a broken symlink.
Boot back into the recovery/install disc and use terminal to rm the symlink and mkdir your home folder of the same name. (you may need to chown this to your user) ** if you can also use rsync from this terminal, skip the Guest step and use rsync now.  I could not**
Do a regular boot, once logged in, turn on Guest login, logout and back in as Guest
Open terminal and su to your user.
Use rsync directly to the TM volume and restore all your home folder.
Check and make sure permissions are correct, reboot!
Everything should look just as it did before you removed your first/second HDD.  Turn off Guest login.


Never symlink your home folder!  While this worked fine, it made recovery a PIA! rather, symlink your individual folders like Documents, Music, Photos, Movies, etc.  It doesn't look as clean, but in the end, it is safer.

If my "data" drive had gone down, I would have had the same issues as I did with this. A system I can not login to.