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Backing up two Macs to the same external drive

Hi all,


I would like to backup two different Macs running Big Sur with two different Apple IDs to the same external hard drive.


After having run the first backup, I connect the drive via USB-C to the second Mac. A popup appears, asking me if I would like to create a new backup or if the computer should claim the already existing backups on the drive.


When I click on "New Backup" it tells me set up a new Time Machine password, seeming as if it was about to format the drive and set up a new backup.


Therefore, I chose to "claim the existing backups" which was then followed by Time Machine running a backup.


I wonder if this this was the right choice and if there are now two different Macs' backups on the drive from which I will be able to choose in case of a data emergency, or if Time Machine somehow merged the two backups into one - which would be obviously a problem.


Does anyone of you know what this "claiming" the already existing backups means?


Thanks for your support!


Max

iMac 27″ 5K, macOS 11.1

Posted on Dec 22, 2020 2:26 AM

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Question marked as Top-ranking reply

Posted on Dec 22, 2020 1:48 PM

You can backup two Macs to the same Time Machine drive. You would have to rename one of

the Macs to something other Macintosh HD. I renamed mine so the other Mac doesn't get confused as to which Mac is which:



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Dec 22, 2020 1:48 PM in response to Makusuto

You can backup two Macs to the same Time Machine drive. You would have to rename one of

the Macs to something other Macintosh HD. I renamed mine so the other Mac doesn't get confused as to which Mac is which:



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Dec 22, 2020 4:19 AM in response to Makusuto

Time Machine Backup insists on claiming the Entire Drive. The only way I know to do what you want would be to Partition the drive into two Partitions giving a Name to one partition for computer # 1 and a different name to second Partition for other computer.

NOTE: It is not a good idea to do so. Should the drive itself fail / malfunction the BAckups for Both computers would be lost. Much better to have two separate drives dedicated each to only one computer

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Dec 22, 2020 10:55 AM in response to PRP_53

Thanks for your quick response. I’ve seen tutorials online that stated that it is indeed possible - even connecting the drive to one Mac and accessing it via network by the others. They even included screenshots showing that time machine just adds another folder for every Mac on the drive. So you guys are definitely sure it’s not going to work? Would be a great feature any way.

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Dec 22, 2020 11:21 AM in response to Makusuto

I am sure it would work.If you re-read Mr. Phillips' comments, he is suggesting that two drives provides increased safety. One drive with two partitions will also do the job. But, when that drive fails, as all drives eventually do, the you could loose two back ups. I personally would never place two back up files on the same unpartitioned disk or on a disk that had other data stored on it. People do this and they often experience problems. My motto is keep it simple. And finally, disks are so inexpensive these days, why not?

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Dec 22, 2020 12:34 PM in response to Ronasara

I’m aware of potential safety risks (even though in over 20 years not a single drive has died on me), but the background of my question is that I bought a huge external drive and wanted to use it to backup my gf‘s MacBook from time to time too. Without the hassle of separate partitions etc., which I know would work.

Therefore, my question simply was, what Time Machine does when I click „claim already existing backups“. I don’t find any info about that. Does it merge the new with the already existing backups on the drive, or does it create that multiple folder structure for the different devices (which would be what I’m looking for)?

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Dec 22, 2020 12:56 PM in response to Makusuto

I understand what you are attempting to do. Since it is a Time Machine question, I can't really address it as I do not use Time Machine for backing up my computers. Why not give it a try for a short period of time to test it and see how it suites you? Then you will know and better understand your "system". In other words, test it out.

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Dec 22, 2020 1:48 PM in response to Makusuto

We understand what you desire to do and why, but, with any shortcut there are pitfalls. Be prepared with a Backup Plan ( no pun intended ). If a really plan is to be in place, get two drives and make Bootable Clones of each device ( yours' and GF ) each to separate drives. Then and only then experiment with using one drive for two computers using Time Machine Backup. If that does not work and something really goes south, the bootable Clone to the rescue.


Just an opinion. Good Luck

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Backing up two Macs to the same external drive

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