After reading about making this big upgrade, from High Sierra to Big Sur, I still have a question regarding a final Time Machine backup of my High Sierra OS. After making the final backup before the upgrade, a poster said to no longer use the backup drive with the new OS. Is this true? Won't Time Machine simply start erasing the older backups as usual? Thanks.
iMac 27″, macOS 10.13
It is not necessary to do that. Upgrading macOS will cause the TM backup drive to be reformatted APFS without any loss of data or its backup history.
However, there are valid reasons to suspect TM needs a copious amount of free space to accomplish the conversion. Since TM backup drives normally operate at or near capacity, there is a distinct possibility TM will report an inability to back up due to insufficient space. That leads people to incorrectly conclude it is not erasing older backups. If TM can do that while retaining its guaranteed minimum of one and only one complete, restorable system backup and perform the conversion, it will.
That is the more accurate description: You can use the same backup drive, but you may not be able to. Besides, it is a good practice to use more than just one backup drive for Time Machine, regardless of the macOS upgrade. The most conservative approach is to obtain at least one additional backup drive and add it to Time Machine. You do not have to remove the existing one, but be prepared if TM complains that it is full.
It is not necessary to do that. Upgrading macOS will cause the TM backup drive to be reformatted APFS without any loss of data or its backup history.
However, there are valid reasons to suspect TM needs a copious amount of free space to accomplish the conversion. Since TM backup drives normally operate at or near capacity, there is a distinct possibility TM will report an inability to back up due to insufficient space. That leads people to incorrectly conclude it is not erasing older backups. If TM can do that while retaining its guaranteed minimum of one and only one complete, restorable system backup and perform the conversion, it will.
That is the more accurate description: You can use the same backup drive, but you may not be able to. Besides, it is a good practice to use more than just one backup drive for Time Machine, regardless of the macOS upgrade. The most conservative approach is to obtain at least one additional backup drive and add it to Time Machine. You do not have to remove the existing one, but be prepared if TM complains that it is full.
Thanks, John. I will see how much space is left on the Time Machine backup. (I ran into that fullness issue with an older TM drive, even without a big update.) I used to have two (one kept off-site) but now just have one since I also use Backblaze. Never enough, I suppose. Thanks!
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You have an opportunity to record some valuable observations regarding free space before and after the upgrade, as well as how much backup history will be deleted, and other relevant data. I neglected to do that given the number of systems and upgrades over the years.
That is a really interesting idea!
Upgrade from High Sierra to Big Sur
