Time Machine backup on a partition - Problem

Hi there!

I am using my M1 for a few weeks now and I want to start running backups for it. But Time Machine won’t help me :frowning_face:

I do have a SanDisk 1TB SSD. But I don’t want to use it all. I think 500-750GB would be enough. So I can use the rest as a normal volume.

That’s how I formated the whole drive. Now Time Machine works fine. I can use this drive as a backup drive. But the moment I partition the disk into 750GB Mac OS Extended for Time Machine and 250 GB ExFat for the Volume, Time Machine won’t let me use the partition as destination.

Can anybody tell me what I am doing wrong?


I am not 100% sure about the cause for this issue, but Apple’s wording is interesting on this topic:

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. If the disk is a Mac OS Extended format disk that contains an existing Time Machine backup, you aren’t asked to erase and reformat the disk.

So, while Mac OS Extended (Journaled) still is no problem for Time Machine for already existing Time Machine Backups, Apple wants you to choose APFS for new Time Machine Backups.

Something else: do you have a reason for choosing ExFAT for the 250 GB volume? ExFAT is nice for external drives, especially when they are used in combination both with PCs and Macs, but I do not think that this will work as long as the whole drive contain volumes with different file systems.

My suggestion would be to just go with APFS for the whole drive - partitioning it with several APFS volumes (or containers) should be fine. But I am not sure if the mix (ExFAT/APFS) is a good idea.

I might be wrong, though. :slight_smile:


One more thing! Welcome to the MPU community! :wink:

1 Like

I didn’t even know you can format Disk partitions with different file system. I usually just choose APFS for all partition and reserved one for Time Machine backup.

Just basing it off experience from my old workplace as our team used a combination of Mac and Windows laptop. Our IT usually provides us different drives for backup specifically for each OS. There’s also another flash drive formatted in ExFAT if we needed to swap large files.

Not sure why it doesn’t work but I’m going to caution you about using backup drives for multiple purposes. Time Machine doesn’t need a SSD. Spinning drives are dirt cheap. Get a couple to use as backup drives and save the SSD for a clone or where you need the speed.

When you store data on a backup drive how are you backing up that data?

On my Intel MBP I’m using APFS formatted spinning external hard drives for TM backups. On each drive I have a separate container (using 2TB of the disk’s 8TB) for TM. It works quite well. I don’t know why a similar setup wouldn’t work with a silicon Mac and an SSD.

You can’t put more than one TM backup, however, on each disk. Two TM backups on the same disk won’t work even if they are put in separate containers, each used exclusively for TM.

1 Like

You are right, of course :smiley:

I’ll take one of my spinning disks to use as a backup drive and use this SSD for storing other stuff.

What do you mean by " backing up that data"? I do have some online storage at backblaze, some data is also uploaded to icloud and onedrive. I am currently on my way to a better backup solution.

If you have a single drive that contains both backups and other data, you have a single point of failure. If you backup the data portion to the backup portion a single drive failure takes out both the data and the backup.

When devising a backup strategy I like to enumerate the risks I’m protecting against. Then I decide how best to recover from those scenarios. Common ones include:

  • Stupid user tricks - deleting wrong file, overwriting files, etc
  • Software failure - OS upgrade gone bad, malware
  • Hardware failure - all hardware breaks eventually
  • Disasters - fire, theft, terrorist attack, floods. Varies by location - wildfires aren’t likely in my location but current fires in California should be a lesson. Looks like you’re in Germany - the recent, unprecedented floods there are another good example.

Finally, any good backup strategy requires testing. Before I retired I was involved in disaster recovery testing. The test would often include bringing up the offsite data center and resuming operations without specified people being available. I use BackBlaze and periodically test getting files back from them. Haven’t tried the “ship me a hard drive” option yet but it’s in the plans.

1 Like