Mac – Does Time Machine reserve additional disk space

time-machine

I have a 1.25TB partition that I use for Time Machine backups. When I am in the system preferences for Time Machine on my Mac, it states there's 525GB of 1.25TB available. But when I browse to the partition, there's only two sparse disk image bundles present (one for my wife's laptop and one for mine), and the total size between the two of them is only 83GB. So why does Time Machine think there's already almost 750GB of disk space already being used? Does the Time Machine partition reserve space for future use and adjust the report of available disk space accordingly?

edit

Here's the (relevant) output from df:

Filesystem                                         Size   Used   Avail    Capacity   iused     ifree       %iused  Mounted on
...
//foobar@Extreme._afpovertcp._tcp.local/TIMACHINE  1.1Ti  764Gi  401Gi    66%        200229312 105076638   66%     /Volumes/TIMACHINE-1

Best Answer

Time Machine does an incremental backup. Thus it doesn't delete saved filesystem-objects that are changed on the source, but rather adds them up. Time Machine offers an interface that let's you browse through your backup history. You can access it through context-menu of the Time Machine-icon in the menu bar. If it ain't there, you can activate it in the system preferences.

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