Using external HDD for Time Machine in Big Sur with APFS. Two partitions?

[NewUsername]

I have a 4TB external HDD. I want to use 2TB for Time Machine and 2TB for my own files. I use Big Sur (M1 Mac) and I want to use APFS on both partitions.

However, I find conflicting information about how to do this. Should I partition? Different containers? Different volumes? Can I set the maximum size of each volume, or will Time Machine eventually eat through the entire 4TB? Things seem to be changed with APFS and Big Sur, so it isn’t clear to me at all.

Does anyone have this kind of configuration, and explain how to do this? Or should I just get a dedicated Time Machine external HDD?

 

[Apple_Robert]

I don’t think you should do a split partition with TM and personal files. If the drive were to get corrupt or die, you have lost a lot of important files. In my opinion, you should use a separate drive for each.

 

[NewUsername]

I don’t think you should do a split partition with TM and personal files. If the drive were to get corrupt or die, you have lost a lot of important files. In my opinion, you should use a separate drive for each.

My idea is to use the separate 2TB partition for the current backups I have. Right now I just copy important folders to my external SSD once in a while, but unsurprisingly that SSD is now almost full. So I would like to move these backups to the external HDD as well, but on a second partition (so I have just one drive for all backups).

 

[white7561]

First. Format the drive to apfs. Then add volume within the same container. It should work then. Choose one for TM and one for your drive. It'll share the storage

 

[0128672]

First. Format the drive to apfs. Then add volume within the same container. It should work then. Choose one for TM and one for your drive. It'll share the storage

I do this and it works well. I even use the non-TM volume for manually backing up files from my iPad.

 

[chabig]

Your choices are:

1. Use two partitions, each with a single container and single volume.
2. Use one partition, with a single container and two volumes.

Both will work. The difference is that the two partition method limits the maximum size of your Time Machine backups and the two volume method does not. With two volumes, all of the space will be shared, which is more efficient, and a plus in my opinion. Over time, your Time Machine backups will grow, but very slowly. I wouldn’t worry about it eating up your space.

 

[Buadhai]

I have a question about how best to accomplish switching to APFS for Time Machine.

I have a 4TB external drive (WD Elements). Currently it has two HFS Volumes; one for backing up another external drive and one for TM. It also has an APFS container which I use for a CCC backup of the boot drive.

I just installed Big Sur and would like TM to backup to an APFS volume. I'm not concerned about retaining the old TM backup data. Starting fresh would be fine. Should I "erase" the existing TM volume and change to APFS, or should I use "partition" to change the TM volume to an APFS container?

 

[svenmany]

I share a container between my CCC clone and another volume of miscellaneous data. It seem efficient since I don't really see the CCC clone growing so much as to squeeze out the miscellaneous data.

But, I would not do such a thing with Time Machine sharing with space with another volume. My Time Machine volumes alway fill up. Invariably Time Machine has to prune old backup sets. A Time Machine backup would certainly take up all the space, leaving no room for the other volume to contain more data.

I do understand that chabig's experience is different than mine. Perhaps my data changes more often causing Time Machine backups to grow more quickly.

 

[circatee]

A while back, I asked a similar question; using a SSD eternal for Time Machine and data storage.
To say people hammered me about it, is an understatement.

Alas, nice to know I am not the only one who has thought about this, as a process.

 

[AlteMac]

Putting all your data on an external drive is perfectly fine -- as long as you have a back-up plan. Having Time Machine and data on the same physical disk is not a back up plan. Disks fail, even SSD's and the OP was using a 4TB external, which is likely a spinning disk. For spinning disks, it is a question of when, not whether, it will fail and when it fails, all the data will be lost. Disk storage has become much more affordable and it makes more sense to have a dedicated disk for Time Machine and a dedicated disk for data. If any one of those disks fails, it is an inconvenience but not a catastrophe.

 

[svenmany]

I think I kind of missed the "back-up plan" angle of the OP's post. I thought the only question was how data and TM can share space and the strategies to use for that sharing.

The OP didn't reveal their total backup strategy. Certainly, if the OP meant for that single disk's TM to provide a backup of that same disk's data, then there had better be some other backups to provide redundancy. Keeping data and its backup on the same physical device exposes both to the same hardware failure risk.

 

[NewUsername]

I think I kind of missed the "back-up plan" angle of the OP's post. I thought the only question was how data and TM can share space and the strategies to use for that sharing.

The OP didn't reveal their total backup strategy. Certainly, if the OP meant for that single disk's TM to provide a backup of that same disk's data, then there had better be some other backups to provide redundancy. Keeping data and its backup on the same physical device exposes both to the same hardware failure risk.

Yeah my initial post wasn't too clear when I see it now.

This is how it works for me now:

Internal SSD: almost everything, also in iCloud
External SSD: Music library and ripped DVDs
External HDD: manual backups of both internal SSD and external SSD

The external HDD has 4TB so I was considering splitting it in two, keeping 2TB for the manual backups and 2TB for Time Machine. Though on a second thought I don’t know if 2TB for manual backups will be enough long-term, so I will probably just get another HDD for Time Machine later on. External HDDs are quite cheap. Or I just leave it like it is. Since I have the files in iCloud Time Machine isn’t that important for me for backups (and I don’t care so much about the travel-in-time aspect). Even if everything fails I still have regular manual backups.

 

[svenmany]

Seems like you know what you're doing.

I think you're right to get a second disk for TM. I use a docking station for such things and put full-size disks in them.

I do want to add something about a constant pain point for me. I connect 3 drives via USB to my MacBook Pro. The laptop handles it terribly. It can take up to a minute to mount the drives and the same amount of time to unmount and eject them. So, for me, that is one downside to adding more external disks to the mix.

 

[Apple_Robert]

Seems like you know what you're doing.

I think you're right to get a second disk for TM. I use a docking station for such things and put full-size disks in them.

I do want to add something about a constant pain point for me. I connect 3 drives via USB to my MacBook Pro. The laptop handles it terribly. It can take up to a minute to mount the drives and the same amount of time to unmount and eject them. So, for me, that is one downside to adding more external disks to the mix.

It might be the docking station you are using that is the problem. My OWC Thunderbolt 4 dock is quick to load etc.

 

[svenmany]

It might be the docking station you are using that is the problem. My OWC Thunderbolt 4 dock is quick to load etc.

I don't think so, but you never know. I don't want to hijack this thread discussing my experiences too much, but it could provide information that influences the OP's decision making with regard to multiple disks.

How quick is quick? Do you have multiple disks and multiple volumes per disk? I have 3 disks and 3 volumes per disk. All three of my disks have a single APFS container with two volumes and a single HFS+ volume for TM.

When I'm away from my desk I carry a single SSD for TM. Even just that ejects slowly. Again, it has three volumes.

 

[Apple_Robert]

I don't think so, but you never know. I don't want to hijack this thread discussing my experiences too much, but it could provide information that influences the OP's decision making with regard to multiple disks.

How quick is quick? Do you have multiple disks and multiple volumes per disk? I have 3 disks and 3 volumes per disk. All three of my disks have a single APFS container with two volumes and a single HFS+ volume for TM.

When I'm away from my desk I carry a single SSD for TM. Even just that ejects slowly. Again, it has three volumes.

I currently have 4 drives connected to my dock and each one of them has a single volume. As to speed, I would says 2 - 3 seconds.

 

[svenmany]

I currently have 4 drives connected to my dock and each one of them has a single volume. As to speed, I would says 2 - 3 seconds.

Then maybe it's the multiple volumes per disk that matters. Whenever I eject, the OS asks me whether I want to eject all volumes or just one. Or it could be the USB on my laptop. (It is the third logic board in 3 years.) Maybe the mid 2018 models have some idiosyncrasy.

So, either a cautionary tale or a tidbit of information to ignore.

 

[Buadhai]

it makes more sense to have a dedicated disk for Time Machine and a dedicated disk for data.

Are you saying that every backup should be on a separate physical drive? I have a boot volume and I have an external volume for media and other data. I have a Time Machine backup of the boot volume and two CCC backups of that same volume. I have two CCC backups of the external volume. So, I should have five separate physical drives for this backup scheme? (I also have Backblaze for offsite backups of everything, plus several cloud services for redundant offsite backup.)

 

[Apple_Robert]

Are you saying that every backup should be on a separate physical drive? I have a boot volume and I have an external volume for media and other data. I have a Time Machine backup of the boot volume and two CCC backups of that same volume. I have two CCC backups of the external volume. So, I should have five separate physical drives for this backup scheme? (I also have Backblaze for offsite backups of everything, plus several cloud services for redundant offsite backup.)

In my opinion, it would be optimal to have 3 backups (to different places) for your internal Mac drive and depending on the content of the external drive, 2 - 3 backups as well. I use 3 different cloud providers and I also backup locally to two different places for 2 of my 3 Macs. My process may seem overkill to many here but, I believe in being prepared for the worst as best I can.