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I have a Macbook Air that has 2 partitions on the hard drive. One is for Yosemite (450GB) named "Macintosh HD" and the other already has Mojave (50GB) on it named "Macintosh HD 2".

When upgrading the Mojave to Catalina, I wanted to back up the Mojave partition ("Macintosh HD 2") and upgrade it.

But when I plugged in an external hard drive named "Seagate2TB", Time Machine started to back up hard drive 1 first (450GB) "Macintosh HD". Since I already set and boot up using Mojave, I restarted the machine, and ejected the 450GB partition "Macintosh HD", but when Time Machine started again, it still was backing up some 410GB of data, which means "Macintosh HD" is included.

So I went to Time Machine's Preferences, and clicked on Options, "+", and chose what to exclude: "Macintosh HD".

Next I rebooted the Macbook Air and wait for the back up to start, and it again, reported backing up 410GB of data.

How can "Macintosh HD" be excluded?

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  • I checked it is just Macintosh HD and Macintosh HD 2. They are different and quite general... what do you mean "compromising" anything? Oct 26, 2019 at 9:11
  • Question: "How can Hard Drive 1 be excluded?" Oct 26, 2019 at 9:19
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    IMO both partitions have the name Macintosh HD, except that one is mounted as Macintosh HD 1 (or 2). Simply rename the boot partitions/volumes to SystemYos and SystemMoj, then exclude SystemYos.
    – klanomath
    Oct 26, 2019 at 9:23
  • Could you replace all the anonymous names of partitions in your question with their real names?
    – dan
    Oct 26, 2019 at 9:23
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    If you mount several volumes with the same name (eg Macintosh HD) then the first volume mounted (usually the boot volume) keeps the original name and all other volumes' mountpoints are renamed to Macintosh HD 1/2/3 automatically/temporarily to make them distinguishable. Or the other way round: mount points mustn't have the same name. The volume names keep the same though.
    – klanomath
    Oct 26, 2019 at 9:28

1 Answer 1

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Your problem is a consequence of an over simplified vision of users from Apple: a user has one uniq computer with one uniq partition then name it with a simple and uniq name "Macintosh HD".

Once you start to have external disks, different versions of OS on the same disk, you should carefully avoid all the failures this over simplistic naming scheme will led you to.

Change all your partitions names with a very clear and really unambiguous name for you and forever.

My personnal use is as follows: every disk partition is named from the computer name it is used on ex.: coriolis, the partition number ex.: 1, its actual capacity, ex.: 250 Gb and the version of the OS it is used on, ex.: High Sierra for a production OS or 10.14.1 for a test one.

Ex.:

coriolis 1 250 Gb High Sierra
coriolis 2 250 Gb 10.14.1

All my computers, all my external disks have a different and uniq name registered at time of their 1st formatting.

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  • @klanomath: feel free to make another answer since you righteously analysed the problem, I'll remove mine.
    – dan
    Oct 26, 2019 at 12:53
  • how do you list the names such as coriolis 1 250 Gb High Sierra? Is it either in the left side panel of Finder, or inside of the Disk Utility app? By the way, sometimes I would not like to use the OS's name, such as High Sierra in the partition name, because what if you upgrade that partition to Mojave and rename the partition to Mojave, then would some of your symbolic links (or some other mechanism) fail to work? If you don't rename, then it keeps on having the name High Sierra, which is not correct. Oct 26, 2019 at 13:19
  • I do the naming with Disk Utility. When I do an upgrade of OS, I upgrade the partition name (from DU or the Finder) as soon as the OS upgrade is tested approved for running. All symbolic links within the root partition should use / and nothing else. This might be the reason I never hit a problem 😊.
    – dan
    Oct 26, 2019 at 13:37
  • @dan I don't wanna write an own answer (other things to do: funeral of a related) but I definitely would have written a different answer (neither blaming Apple or a user). Something in a commanding tone – I'm german :-) - do this, do that & a tiny explanation (more or less my comments1 & 2 pimped)
    – klanomath
    Oct 26, 2019 at 22:46

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