Time Machine Problem (Always deleting and re-backing up)

[Astral Cars]

The last few days, Time Machine seems to be deleting pretty much the entire backup and the recopying it. My backup hard drive is just barely big enough to accommodate what it's backing up, so at this point I guess TM's just used to do my backups for me and I don't really expect it to have any historical backup value. The problem is that it spends hours backing up everything and then when it's finished I notice the drive is almost empty. If I look at the files, it's got all the folder structure, but (for example) all of the music files themselves that should be held within these folders are not there. I see that as a pretty useless backup. The next backup after it seemingly deletes it all is about 9GB and the the next one after that is around 56GB, when it finishes that it deletes it again and starts this process over.

Does anyone know what the problem is here? I'm confused and a bit annoyed (and starting to get paranoid that I'm going to lose files as a result).
Thanks.

 

[imfrog2002]

It's because time machine deletes backups when it's full. I'd say to invest in a new HDD. For about $100 you can get one on Apple that would be large enough. That's just my opinion. I spent $125 and I got a 500GB external. It's been perfect for backups. That's my suggestion.

 

[Astral Cars]

So TM will just erase the oldest and re-write the current rather than saving whatever is the same? That seems strange.