Formatting an external SSD for Time Machine and other uses?

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D. Ryder Author

Level 1

10 points

Formatting an external SSD for Time Machine and other uses?

Asking people much smarter than me...

I'm currently using a 4TB external HDD for the backups of a 1 TB internal SSD plus extra storage. It's partitioned into

1 TB for CarbonCopy Cloner clones,
2 TB for Time Machine backups, and
1 TB for offloaded files and general extra storage.

I'm about to upgrade that HDD to a 4 TB NVME SSD for improved speed.

I was planning to format the SSD as APFS. The article linked below from Apple recommends APFS for Time Machine, but notes that the Time Machine backup requires it's own volume.

Types of disks you can use with Time Machine on Mac - Apple Support (CA)

From that link: "APFS or APFS Encrypted disks are the preferred format for a Time Machine backup disk. If you select a new backup disk that’s not already formatted as an APFS disk, you get the option to erase and reformat it... Note: The entire APFS volume is reserved for Time Machine backups. If you want to store files other than the Time Machine backup on the same physical device, use Disk Utility to create an additional APFS volume on the disk. The two volumes then share the available space."

When I get the new SSD, should I:

Create 3 partitions, formatting each to APFS, then creating a single APFS volume inside each? Or,
NOT partition it, and rather, just create 3 APFS volumes, dedicating one to each of the 3 uses?

Thanks for your advice.

MacBook Air (2020 or later)

Posted on Apr 2, 2022 5:45 PM

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Answer 1

steve359

Level 6

17,187 points

Apr 2, 2022 9:20 PM in response to D. Ryder

FYI ... and assuming you do not know yet ...

Under Monterey CC-clones are less useful as "alternate boot" (I think) than as "simple backups". CCC cannot update/maintain the "Sealed System Volume" in a bootable clone due to Apple heightened security. So bootable clones can only be "point in time" and must be rebuilt from scratch when the cloned system changes enough to make the bootable clone unusable.

The constant rebuilding would recommend a separate and dedicated drive so that "other storage" is not risked.

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Answer 2

tbirdvet

Level 6

17,277 points

Apr 3, 2022 6:33 AM in response to D. Ryder

I agree with all the above comments. I use NVME drives but always have one dedicated to TM. With each OS upgrade TM becomes more picky and wants to be a dedicated drive. I use CCC to make one bootable drive and another just for data that I store at a different location. The bootable drive work but like stated above they need to be updated with each OS change to be reliable however I also find a bootable drive to have less value with my M1 Mac and Monterey. If my internal drive fails the external will not boot anyway.

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Answer 3

D. Ryder Author

Level 1

10 points

Apr 2, 2022 8:09 PM in response to steve626

I’m in that risk now (total loss if the HDD fails — and I’ve already experienced an HDD failure) with this approach. I am OK with that risk. I may retain the HDD for CC clones and (more likely) extra storage, but won’t use it for Time Machine backups. I’ve been successfully using 2x sized Time Machine backups with no issues for years. But I agree: by using this approach, I’m at risk.

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Answer 4

D. Ryder Author

Level 1

10 points

Apr 2, 2022 9:39 PM in response to steve359

Yeah, I was disappointed when Apple’s security aspects made CCC a bit less useful. But I understand what Apple did, and why. Still a fan of what value CCC adds. And… have had issues with Time Machine backups in the past. Recovering a file? Great. Recovering everything? CCC much better. Belt and suspenders. Yet… I get that putting them on the same physical device is suboptimal.

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Answer 5

Owl-53

Level 10

103,843 points

Apr 3, 2022 2:27 AM in response to D. Ryder

Regarding Bootable Clones via CCC - would suggest following this question. The Topic does not pertain to TM Backup drives but does reference Bootable Clones.

CCC has cautioned, since Monterey 12.3 and beyond to Not attempt a Legacy Clone in CCC 6.1.1 as it will fail because of some changes Apple has Introduced in 12.3 and beyond.

This is covered in that question and special attention to contributor @ Kurt Lang response on page two of the question

Broken Monterey System Volume Seal

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Answer 6

D. Ryder Author

Level 1

10 points

Apr 3, 2022 8:12 AM in response to Owl-53

I don't use CCC to make bootable clones. I used to, until it became nearly impossible. Pretty sure I gave up at Monterrey, but it could have been sooner. Still like the program and what it does, though.

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Answer 7

steve626

Level 6

14,361 points

Apr 2, 2022 7:09 PM in response to D. Ryder

I would not partition it nor would I create multiple volumes. If the physical drive were to fail (they all do fail eventually, it is a matter of when, not if), you would immediately lose your backups, your clones, and those other files as well. This would be a "single point failure," something to absolutely avoid.

I would dedicate the entire drive to Time Machine. The Time Machine drive should be 4x the size of the source drive. I would get other drives (mechanical are ok if SSDs exceed your budget) for the other things. This mitigates the risk of drive failure -- any drive can fail, you still have copies (assuming you have copies of the misc storage files as well). They need not all be 4 TB; the clones need only be slightly larger than the source drive, and for misc storage I would think 1 TB should be enough.

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Formatting an external SSD for Time Machine and other uses?

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