One Time Machine drive for two Macs?

[apostolosdt]

I'm a bit confused and I hope for some kind or illumination.

I use a 4TB platter drive as a Time Machine for my Mini M1. It is formatted as extended journaled. I have just acquired a 2017 iMac and I was planning to use the drive as the TM for both Macs. I only keep the OS and the apps internally---all the data are in the Cloud. Therefore, with their storage capacity of 256 GB and 512 GB, repectively, I figured out that backups would occupy very little space (I manually backup).

But reading in the Internet about that has made me wonder if I am doing the right thing, if it's at all possible. So, please, could you clarify on these?

1. Is is possible to use one TM drive for two Macs running Sonoma and Ventura?
2. If yes, would it still be possible if I had formatted the disk as APFS?
3. Is it a sound practice, or should I avoid it; that is, run two separate disks?

Thanks, guys.

 

[kitKAC]

I'd go with two separate disks, so you can leave them permanently connected to each machine.

 

[apostolosdt]

I'd go with two separate disks, so you can leave them permanently connected to each machine.

Sure, good point, thanks. But my question still holds: Is it OK to use two Macs with the same TM?

 

[Ifti]

Partition the disk and set each partition as a backup destination for each mac.

Even so, I wouldn't recommend it - if one disk goes down you lose backups from 2 systems, irrespective of your main data being in the cloud.

 

[apostolosdt]

Both pieces of advice are wise and I have followed them already (abandoned my original plan).

But still... my original question holds: Is it OK to back up two Macs on the same TM without partition?

 

[Rob__Mac]

But still... my original question holds: Is it OK to back up two Macs on the same TM without partition?

Yes. I use a NAS to backup both of my Macs, no issues. It makes a .Sparsebundle for each computer.

 

[apostolosdt]

Rob__Mac, thank you very much!

 

[gilby101]

But still... my original question holds: Is it OK to back up two Macs on the same TM without partition?

Yes, each Mac can use a different APFS volume for TM.

But, I would be wary if the two Macs were running different versions of macOS. This is because the more recent macOS might make changes to the APFS container format which the older macOS doesn't fully understand. The problem might not come to light until you are trying to do a Migration Assistant recovery.

I suspect (you would need to test, including recovery) that there would be no problems with Sonoma and Ventura backups in the same partition/container. It would be safer to use separate partitions.

 

[apostolosdt]

Thanks. I have heard about APFS’s unique behaviour. I was hoping the extended journal format would do better, and maybe it will.

 

[kitKAC]

Yes. I use a NAS to backup both of my Macs, no issues. It makes a .Sparsebundle for each computer.

Time Machine only uses .Sparsebundle's for network volumes though.

 

[Fishrrman]

Just because you can do it, doesn't mean you should.

I get the impression from your avatar, that you're into photography.
If so, I would not trust "two computers on one tm drive" to be a sound backup strategy.

 

[apostolosdt]

Thanks, Fishrrman, and yes I photograph, but as a hobby. By now, I've been convinced that running one TM for two computers is not a good idea.

 

[hutleytj]

Just because you can do it, doesn't mean you should.

I get the impression from your avatar, that you're into photography.
If so, I would not trust "two computers on one tm drive" to be a sound backup strategy.

Not a safe enough strategy. You cannot have too many backups. I run 3 backup disks (each 4 or 5 TB) simultaneously for my one MBP.

 

[ItWasNotMe]

Not a safe enough strategy. You cannot have too many backups. I run 3 backup disks (each 4 or 5 TB) simultaneously for my one MBP.

Time Machine is not an archive, It decides when to delete things not you. If you really need to keep something then use another method. Having TM on multiple disks does not address this

Once thinning starts, there is no guarantee you will have a copy of a file however many TM disks you use, and it might not take long for that to happen.

For example, let's say Time Machine keeps weekly backups on a cycle that is Sundays. You create a file Tuesday and 'accidently' delete it the following day. Whilst you still have the daily backups you can still get to the Tuesday copy. Once the days are thinned into weekly backups then you'll have the files as at the Sunday preceding that Tuesday (before you created it) and the following Sunday (by which time you deleted it) and nothing in-between. The file you created on that Tuesday no longer exists.

Even if the multiple disks run on different thinning cycles, it's always possible to construct a scenario where you loose a file you wanted to keep.