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Use attached drive for Time Machine for that computer and another

I want to use a 10TB drive to backup the iMac that it is attached to for Time Machine and also use that drive to back up other Macs using the local network. As a slight complication the drive is partitioned because another app is backing up that needs a separate partition (Mylio).


If I follow Set up file sharing on Mac - Apple Support to allow other computers to backup to the partition by creating folders for each computer and setting "advanced file sharing options" for the folder for TM backups, I can backup other computers to the "backup" partition.


However I am unable to use that partition to backup the iMac.


If I erase the partition and backup the iMac to the partition I can't use it for the other computers.


Is this possible?


Posted on May 5, 2022 3:42 PM

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Posted on May 5, 2022 5:46 PM

If you back up a locally connected Mac, you cannot use that partition for anything else.

You would have to create another partition or create a Volume using Terminal--as far as I'm aware, Apple hasn't fixed Disk Utility to allow creation of a Time Machine Volume.


You don't need separate folders as a network backup will create a sparse bundle disk image for each Mac backing up over the network.

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Question marked as Top-ranking reply

May 5, 2022 5:46 PM in response to SoCalMtnBiker

If you back up a locally connected Mac, you cannot use that partition for anything else.

You would have to create another partition or create a Volume using Terminal--as far as I'm aware, Apple hasn't fixed Disk Utility to allow creation of a Time Machine Volume.


You don't need separate folders as a network backup will create a sparse bundle disk image for each Mac backing up over the network.

May 5, 2022 5:59 PM in response to Barney-15E

Thank you. I began to assume that since I tried all the combinations and my reading of Apple's documentation didn't mention the possibility.

I now have three partitions on an external hard drive and it seems to be working (will have to wait to make sure backups complete)

  1. locally connected iMac
  2. for other Time Machines backups. I did create folders and see that there is a sparsebundle. I had done this before reading your post because I was afraid that maybe only one TM backup would be allowed in the partition and I was tired of starting or creating backups and waiting for them to complete and then find out I had to erase the partition. Overkill at this point, but I don't think it's costing much.
  3. for Mylio backup/"Vault" which requires its own partition. Mylio is a multi-platform application so often doesn't use all of macOS capabilities.

I rather have as few partitions as possible since it means I have to change the size if one partition needs more space and I may have too large a partition and never use it.

May 5, 2022 6:02 PM in response to Barney-15E

Rant: "If you back up a locally connected Mac, you cannot use that partition for anything else." I didn't notice that in the Apple documentation or when starting a TM backup in a partition. Maybe I missed it. So many repetitive warnings, but not one for something important. Wanting to use an external drive for many TM backups would seem to be a common situation.

May 6, 2022 9:30 AM in response to SoCalMtnBiker

Adding a bit more information. For my wife's MBP, I set up a folder (as above) and in "Sharing" gave her permission to read-write to that folder. Then right-clicking on the folder set to allow Time Machine Backups. To help us understand what and where that disk is I gave it a name similar to "Wife TM backup on 10TB HD". Seems like overkill, but on her TM preferences clearly shows which backup it is. Because she also has occasional TM backups to drives stored elsewhere.


I could have missed a step or two because of the convoluted nature of this. For example in Sharing a button "Options" is available and then hidden under a right click is "Advanced Options". Options mentions SMB and Windows. Etc.

Use attached drive for Time Machine for that computer and another

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