So I finally upgraded my Macbook to Mountain Lion (from Snow Leopard) a couple of weeks ago. Realised recently I accidentally deleted an important archive folder about a month ago. No problem - go back in Time Machine and restore it. To my horror, two years of backups in Time Machine are gone Here's what happened: On Snow Leopard: I have Time Machine backups going back 2 years. I restore a file from backup about once every couple of months, so I know it's all there and working fine. The size of the TM backup is around 400 GB with about 50GB free on my Time Capsule and on my Macbook I currently have about 350GB of folders being backup'd. (I exclude downloads, films etc, so mostly it's new email, documents etc being backed up) Mountain Lion upgrade: I just downloaded ML from the App Store and followed the default instructions. (I didn't have time to do a clean reinstall). All seems fine. I told Time Machine to warn me if it needed to delete old files to make space. 50GB free seemed enough to handle the OS upgrade, but just in case... Next morning: Time Machine tells me it's run out of space - it needs to back up 180GB but only has 50GB free. I go into TM and every previous backup is gone! There's only the most recent backup left TM didn't warn me before deleting my old backups I checked TM settings and 'Notify after old backups are deleted' is still checked. Luckily I have a backup of my TM backup, a duplicate I made about 6 months ago, so I was able to restore some files from that, but some are still gone Any idea what I can do? Why would upgrading to ML cause 180GB of changes? Looking into the TC sparsebundle in Finder, it does seem that only the most recent backup is still there Guess I just have to cut my losses and start a new set of backups.