Time Machine reports backup disc needs to be 8.78 Tb. I only have a 250Gb system drive???

Question

Thought I'd do a TM backup before installing Mavericks.  It messed up big time!
I backup manually depending on how much stuff has accumulated.  It varies between a few Mb to 3 or 4 Gb sometimes more.  Today Time Machine decided that it wanted to reorganise the backup in some way.  I watched as the available space on the TM disk went up as TM set about the task.  After a couple or three hours TM actually started to do the backup.  The size of the backup being 500Gb or something like that.  Several hours later of listening to my fans working flat out I cancelled the back up with TM reporting that there was 200 odd Gb to go.  No warning from TM to say this was a bad idea.  It had been chuntering away for something like 5 hours.
After halting the backup I thought I'd start the backup again just to see how much more needed to be done.  This is when I got the report that the backup disk needed to be in the order of Tb. And the oldest backup is now Nov 2013.  The oldest backup before this was way back in June 2012 (MacBookPro Rertina mid 2012) when I first bought the computer.
Entering TM I find that even that is not complete. All but a couple of applications have dissapeared as have many other files.
Trouble is I use it as an archive and happily delete files on my hard drive knowing that there is a copy in a backup that pre dates the deletion. 
There is also an earlier backup from my previous machine - again as a rarely accessed archive.  So that's another reason not to reformat.
I'm pretty sure all is lost and I think I just have to bite the bullet and risk not needing anything from the archive.  After all I have CD and DVD backups/archives that go back to the late '90s and I have rarely needed to access them over the years.  The biggest loss will be photos.  ****!
Anyway.  What happened?  Why has TM gone off the rails?  I have done nothing different to what I have done in 5 years or so.  Is this normal behaviour?  If I hadn't have cancelled the back up would TM have slowly rebuilt all my backups as was?
Andy

Answer 1

Trouble is I use it as an archive and happily delete files on my hard drive knowing that there is a copy in a backup that pre dates the deletion.
Before going any further please understand that's a very bad idea. It's beyond Time Machine's scope to do that. It is not an archival system and cannot be made to become one. Time Machine guarantees nothing other than one complete copy of the source volume's contents. Anything erased from the source becomes fair game for Time Machine to delete from the backup, the moment it requires the space it occupies.
Next: I have no idea why the problem occurred, but a first and harmless troubleshooting step is to reset Time Machine by doing the following:
Turn off Time Machine first, and make sure a backup is not in progress.
Triple click to select the entire line, then control-click and select Services > Reveal in Finder. Drag the selected file to the Desktop, or directly to the Trash:
/Library/Preferences/com.apple.TimeMachine.plist
This will not delete your existing backups.
Turn on Time Machine and reselect your backup volume. The effect of deleting that file will cause erroneous values to be shown in the "backing up xxx of yyy" messages until the subsequent backup.
If it's any consolation, terminating Time Machine as you did is not an abnormal user action and did not cause the problem. It may have resulted in inaccurate information being written to the property list, which you will fix by deleting it. It's quite possible that your backups have remained intact. Just remember that anything you delete from the source may no longer exist following the subsequent backup, and that is to be expected.