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What does Time Machine back up-- all files or just the changed ones? If it is just changed/added files, then when TM deletes old backups to make room, how are those added files / file changes preserved?
My understanding is the very first backup made is a full system backup. Then, every hour afterwards only updates are backed up. At some point, TM processes all the day's hourly backups and creates a single day's backup. When TM needs more space, the older dated backups are removed but all current dates are retained.
For example, let's say a TM backup disk has backups from 9/1/18 thru 9/9/19. The backup disk is suddenly running out of space so during the next backup, TM makes room by removing backups from 9/1/18 thru 11/30/18. If a user wanted to restore a file in that time frame, the data is gone. The user can only restore files/folders/system from 12/1/18 thru 9/9/19. Hope this makes sense.
My understanding is the very first backup made is a full system backup. Then, every hour afterwards only updates are backed up. At some point, TM processes all the day's hourly backups and creates a single day's backup. When TM needs more space, the older dated backups are removed but all current dates are retained.
For example, let's say a TM backup disk has backups from 9/1/18 thru 9/9/19. The backup disk is suddenly running out of space so during the next backup, TM makes room by removing backups from 9/1/18 thru 11/30/18. If a user wanted to restore a file in that time frame, the data is gone. The user can only restore files/folders/system from 12/1/18 thru 9/9/19. Hope this makes sense.
Only files that have been written since the last backup.
This explains how TM works:
Thanks! That’s a great article.
You're welcome.
Time Machine backup-- all files or just changes?
