Backup volume
T2M2 doesn’t attempt to check the condition or status of your backups, as stored on the backup volume. However, it does check how much free space there is on each backup volume, and warns you if that is becoming low.
At the top of the report T2M2 states the device and path to your backup volumes used during the period assessed. In versions of macOS up to and including Mojave, it also reports the free space available when each backup was made. That information is not recorded in Catalina.
Below those, T2M2 reports the current free space on each backup volume at present (the time that you clicked the button to Check Time Machine). To help you interpret this, it displays an emoji for the quantity:
⛔️ indicates that free space on that volume has fallen below 10 GB, and you should delete old backups or use a fresh volume as a matter of urgency, or Time Machine will run out of free space soon;
⚠️ indicates that free space on that volume has fallen below 50 GB but is 10 GB or more, and you should free up space on it in the near future, or Time Machine may run out of free space;
✅ indicates that free space on that volume is 50 GB or more, and there should be sufficient for the immediate future unless Time Machine needs to make unusually large backups.
This status indication is independent of the traffic light at the top of the window: it is quite possible for the space warning to be ⛔️ but the traffic light to remain green.
If a backup volume isn’t mounted at the time that you Check Time Machine, it won’t appear in this list. Networked devices (NAS) may also report unexpected results, or nothing at all, depending on how they are seen by macOS.
The tool of choice for thinning and maintaining Time Machine backups is tmutil , although the Time Machine app provides basic tools as well.
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