When that happens, backups will start failing, and this notification will appear after every backup attempt.Ĭlick the Details button in that notification to open the Time Machine pane of System Preferences, and you’ll learn more. In general, this approach works well, since you probably don’t need all the older versions of changed files as long as Time Machine always retains the most recent version in the backup.Įventually, however, even this technique runs into the wall of hard drives having only so much capacity. It warns you when this starts happening and tells you what your oldest remaining backup is. So the first thing that Time Machine does when your backup drive fills up is start deleting those older versions, beginning with the oldest ones. If you modify the same file multiple times per day, every day, you’ll have numerous versions of it in your backup set so that you can go back to any particular version. After that, Time Machine keeps hourly backups for the past 24 hours, daily backups for the past month, and weekly backups for all previous months. On its first backup, Time Machine copies everything on your startup drive to the backup drive. What happens then?īefore we explain, some background.

Time Machine is smart about backing up only files that have changed, but after months or years of usage, the drive will run out of space. It’s inevitable-your Time Machine backup drive is going to fill up.

Mac clear space on hard drive