I got home from work today to see a message about needing 232.79GB to backup but only having ~100GB. Firstly that makes no sense because I "only" have 200GB of files on my hard drive (although obviously the backup would need more), but more importantly there is no way they have all changed since yesterday. I opened the time machine backup and noticed it had deleted every single backup apart from one from last night. The log is full of entries like this From late last night (don't know how far back it goes, console.app doesn't show much further back) until the time when I got home. Has anyone got any idea why it has done this, there is no reason for it that i can work out and now I'm a bit worried it is going to start screwing up backups in the future.