I'm interested in buying an external hard drive. I'd like to know whether if it's possible (and simple if so) to have two separate Time Machine Backups from two different MacBooks at the same time?

  • Have a look at Back up multiple computers with Time Machine, specifically Method No. 1: SneakerNet and Method No. 2: Network Backups as Method No. 3 is for Time Capsule, not a regular external hard drive. Also contrary to what's suggested by Mattia, you do not need to have multiple partitions although that might be handy. The External HDD just needs to be formatted the native filesystem used by OS X, HFS+. Jan 15, 2016 at 16:59
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    @user3439894 I think that backup with two different partitions is better in order to keep track of the files and therefore avoid confusion. And for the utility point of view one partition or two is the same if you use the partitions only for backup.
    – rebatoma
    Jan 15, 2016 at 17:05
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    @Mattia, You're certainly entitled to your opinion, and I don't necessarily disagree with the statement you made in your comment. However in your answer you start by saying "If you make two different partitions in the external HD..." and that is not required as Time Machine is intelligent enough to know which backup folder is for which computer. Anyway, I did say in my first comment "although that might be handy." in reference to multiple partitions. ;) Jan 15, 2016 at 17:13
  • @user3439894 totally agree.
    – rebatoma
    Jan 15, 2016 at 17:17

3 Answers 3


If you make two different partitions in the external HD, you can easily have the two different Time Machine backup in the each partition.

You only need to specify the partition to use for the MacBook during the initial Time Machine setup. Then the Mac would know which partition to use for its backup the next time you connect the external HD. The same goes for the second MacBook.

By doing so you could limit the amount of space taken up by he Time Machines of both Macs.

  • Can I make three partitions; two for Mac Extension time machines, one FAT32 for regular data storage?
    – Ébe Isaac
    Jan 15, 2016 at 16:52
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    Wow, sorry! Used the wrong word, totally spaced out. My question was supposed to be: Are you sure partitioning is even necessary? I thought TM allowed this even without partitioning.
    – Fiksdal
    May 10, 2016 at 7:41
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    @Fiksdal yes you are right. TM allows even multiple backups in the same partition. I suggested the use of multiple partition in order to keep them in a separate way.
    – rebatoma
    May 10, 2016 at 8:05
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    @Mattia Alright. But I think it they are encrypted, then sepreate partitions, are required, right? Anyway, partitioning has the downside that you have that if one backup becomes larger than expected, it's unable to access the free space in the other partition.
    – Fiksdal
    May 10, 2016 at 8:08
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    Alright. Anyway, I think there's definitely a need to partition if encryption is utilized. This is because TM works by formatting the whole disk or partition that the backup is located on, and it can't use the same key for each computer's backup, because they belong to different users (as far as TM is concerned), and are (often) based on different passwords.
    – Fiksdal
    May 10, 2016 at 8:44

You can use an external hard disk formatted with HFS+ as a Time Machine target for several Macs without problems. Time Machine itself will make sure that the data is not getting mixed up by using the name of each Mac as part of the path.


For what it's worth, I have this setup running in a few locations with a single NAS, and multiple machines backing up to it. As long as you specify a separate folder, there is no need to create separate partitions. The backups will be completely separated out, and allow you to connect again, authenticate to the folder, and restore from the backups as needed.

I do have separate user accounts on the NAS, so the network folder is logged into by each machine separately with it's respective authorized user.

  • Does sharing a single partition mean that if one machine backed up more frequently it would grab more of the drive until it was full and the less backed up machine would get stuck with whatever space is left and never be able to force deletions of old backups from machine one?
    – Craig
    Mar 31, 2017 at 0:25
  • If you don't use separate partitions how do you limit the size of each backup to prevent one taking up all the space? I know on OS X server you can limit each backup size but don't think that is possible with NAS/Airport USB disk/Time capsule.
    – malhal
    Sep 7, 2017 at 12:30

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