Time Machine not listing external drive for available backups for 'Select Disk'

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Time Machine not listing external drive for available backups for 'Select Disk'

I have an existing TM backup and am trying to add a second disk so I have multiple backups, something I've done many times before. My MacBook Pro is not listing the external drive when I click 'Select Disk'. The most common cause is not formatting the drive correctly, so I confirmed it's Mac OS Extended format (Journaled). What is really odd is that I have another MacBook Pro with a different Time Machine backup, and when I click 'Select Disk' the disk in question is available to create a backup.

Why would a disk be available to create a TM backup on one computer and not another? I've unmounted and mounted the disk through Disk Utility quite a few times, reformatted the disk with a different name, it's still not listed as available.

Thanks for advice on this.

MacBook Pro 15″, macOS 10.14

Posted on Apr 12, 2021 8:45 AM

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Answer 1

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Nathan_SF Author

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Apr 13, 2021 8:00 AM in response to Grant Bennet-Alder

I was able to re-create the other partition. I had 2 partitions, one for data and one for a TM backup. I copied everything from the data partition to another computer, reformatted the entire drive, recreated the partitions with GUID table, backed up TM to one and copied the data back to the other. A bit convoluted but it worked :)

Overall drive format was Mac OS Extended (Journaled) both before and after formatting. I think the orignal schema was Apple Partition Map.

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Answer 2

Nathan_SF Author

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Apr 12, 2021 7:54 PM in response to Nathan_SF

Resolved by reformatting entire drive (both partitions) and using GUID Partition Table. Thanks for input.

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Answer 3

Apr 12, 2021 9:24 AM in response to Nathan_SF

Drives like the MyBook came with software, and the manufacturer suggested you install that software.

What that software does is to "spare you the annoyance of having to re-initialize the drive" from its factory set Windows New Technology File System (NTFS) or similar unusual (on a Mac) format. Instead, the software they provided would simulate a MacOS drive inside an NTFS file for your Mac.

The downside of this practice is that if the manufacturer's software is not loaded, the Macintosh Volume is not readable. This means that in startup manager, Installer, and in recovery such as after a data loss, the Macintosh Volume will not be visible.

The standard advice given here to all users, including novice users, is to discard the manufacturers software and NEVER use it. "Best Practice" is to erase the drive when new, using only MacOS Disk Utility, and create the fundamental data structures needed for consistent, reliable use by MacOS.

punchline: REMOVE the manufacturer's add-on Drivers, or Restart in Safe Mode.

ERASE the drive by its immutable manufacturer-hadware-name (not just "Macintosh HD ir similar)

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Answer 4

Apr 12, 2021 9:32 AM in response to Nathan_SF

Does the drive mount? is it visible on the desktop? what files are on it? what user is the owner?

.

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Answer 5

Nathan_SF Author

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Apr 12, 2021 9:26 AM in response to Grant Bennet-Alder

Thanks for the tip, the first thing I do when getting a new drive is wipe the manufacturers software. No add-on Drivers, erased the drive completely before using and renamed.

I've also reset NVRAM and SMC.

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Answer 6

Nathan_SF Author

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Apr 12, 2021 10:19 AM in response to Nathan_SF

It mounts and is visible on the desktop. This partition has nothing on it, freshly formatted. Other partition has a data backup (non-Time machine). Like I mentioned, the exact same drive does show up as an available TM backup option on another computer.

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Answer 7

Nathan_SF Author

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Apr 12, 2021 12:31 PM in response to Nathan_SF

I've tried multiple drives that all show up as valid drives for TM backups on other MacBook Pros, but not this particular computer. The computer itself is in a state in which it's not recognizing drives. Any way to reset this from the shell?

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Answer 8

Apr 13, 2021 7:26 AM in response to Nathan_SF

What was the overall drive format before?

Were you able to re-create the 'other' partition after reformatting, or can you only use the entire drive?

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Answer 9

Nathan_SF Author

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Apr 12, 2021 9:03 AM in response to Nathan_SF

MacOS for the computer for which the drive does not show up as an option is actually 11.2.3, not the version listed above. Drive does show up as an option on a different computer that's running 10.15.7, but I don't think this is a version issue. Somehow TM is 'stuck' and won't recognize any additional drives.

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Answer 10

Nathan_SF Author

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Apr 12, 2021 10:18 AM in response to Grant Bennet-Alder

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Time Machine not listing external drive for available backups for 'Select Disk'

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