Mojave Time Machine file format question

[jhinkle]

Hi all,

Please correct me on any of the following information if I am wrong. I'm about to purchase a 2012 Macbook Pro and install Mojave on it. It is my understanding that the laptop's internal drive with Mojave OS on it will be formatted in APFS.

If I do a Time Machine backup and save it to the same internal drive, will the backup be formatted in APFS or HFS+? If the Time Machine backup can be formatted in APFS to the internal drive, great.

If not, and the Time Machine backup file format must be HFS+, I would need to partition the internal drive for space on it to be formatted in HFS+, correct?

But then if I want to actually access a particular Time Machine backup formatted in HFS+, how does that work? Will Mojave convert the HFS+ Time Machine backup to APFS file format so that I can run that backup on the APFS partition of the internal drive that's running Mojave?

These questions originated from my reading that only from Big Sur on can a Time Machine backup be done with an external drive using the APFS file format. So is it correct that when doing a Time Machine backup to an external drive on the laptop running Mojave, that the external drive must be formatted in HFS+? I then have the same question about how it works if you want to access/run the Time Machine backup on the Mojave internal drive formatted in APFS - will it convert the external drive's HFS+ Time Machine backup to APFS so that this can be done?

My last assumption as to how it possibly works is that if a Time Machine backup done on Mojave always has to be in HFS+ format, then the only way to access the Time Machine backup is to access it with an internal drive that is running an OS that is Sierra or earlier? I can't imagine this is true since Mojave can read HFS+ files.

I hope I am making sense, I apologize if these are dumb questions, and thanks in advance!!!

 

[Brian33]

my understanding that the laptop's internal drive with Mojave OS on it will be formatted in APFS.

I believe that is true.

If I do a Time Machine backup and save it to the same internal drive, will the backup be formatted in APFS or HFS+?

It is very unusual to put your backup on the internal drive (i.e., the same drive as the backup source). If the (single) drive fails, you lose both your original files and all of your backups! You should use an external drive for backups (or a cloud/internet backup service).

Perhaps you are you planning on using TM not as a backup but as a versioning system? So you could retrieve older versions of documents?

In any case, for Mojave, the TM backup volume must be formatted HFS+.

If not, and the Time Machine backup file format must be HFS+, I would need to partition the internal drive for space on it to be formatted in HFS+, correct?

Yes. If you insist on backup up to the internal drive I believe you would need to have two actual partitions created before macOS was installed. I say this because I don't think you can add a new partition (and I don't mean an APFS Container) without losing the data on the boot drive.

You would need to boot from either Internet Recovery (NOT the normal recovery volume) or from a bootable installer created on a flash drive. You must select the top-level hardware device in Disk Utility, which is not visible by default (make sure to select "Show all Devices" in the View menu).

if I want to actually access a particular Time Machine backup formatted in HFS+, how does that work? Will Mojave convert the HFS+ Time Machine backup to APFS file format so that I can run that backup on the APFS partition of the internal drive that's running Mojave?

You'll be able to access the files in the backups just fine. I'm not sure what you mean by "run that backup" -- these are not bootable backups. Really they are just copies of all the files on the source volume as of a specific point in time. You can use Finder to drag and drop, or the TM restore interface, or (in a disaster situation) Migration Assistant. In any case, it's macOS that is reading and writing the files -- and macOS (on Mojave) knows how to work with both HFS+ and APFS filesystems. If you want to copy a file from the backup to the boot volume, Finder just uses macOS system calls to read the file from the HFS+ volume, and then tells macOS to write the same data to the APFS volume. There's no drama. It's like Windows copying a file from an exFAT or FAT32 "disk" to an NTFS boot volume. Windows knows how to read and write both formats.

So is it correct that when doing a Time Machine backup to an external drive on the laptop running Mojave, that the external drive must be formatted in HFS+?

Yes. And I highly recommend you do use an external drive for backups.

My last assumption as to how it possibly works is that if a Time Machine backup done on Mojave always has to be in HFS+ format, then the only way to access the Time Machine backup is to access it with an internal drive that is running an OS that is Sierra or earlier?

No, that's not true. Any macOS version can read HFS+ formattted volumes, including Ventura.