Time Machine defaults to backup to my NAS and not to my external time machine formatted drive

Another option is to just continue running the Time Machine backups on the NAS.

Then use CarbonCopyCloner or SuperDuper to make clone backups on the local external drive.

see > https://bombich.com/ and/or > https://www.shirt-pocket.com/

Give this a try: boot into Safe Mode according to How to use safe mode on your Mac and set the default drive to the local external drive andtest to see if the problem persists. Reboot normally and test again.

NOTE 1: Safe Mode boot can take up to 3 - 5 minutes as it's doing the following; 

• Verifies your startup disk and attempts to repair directory issues, if needed

• Loads only required kernel extensions (prevents 3rd party kernel/extensions from loading)

• Prevents Startup Items and Login Items from opening automatically

• Disables user-installed fonts 

• Deletes font caches, kernel cache, and other system cache files

NOTE 2: if you have a wireless keyboard with rechargeable batteries connect it with its charging cable before booting into Safe Mode. This makes it act as a wired keyboard as will insure a successful boot into Safe Mode.

Time Machine will automatically back up to the first available network destination on its schedule, even if a local APFS Time Machine drive is connected. Local drives don’t always get priority unless you start the backup manually or remove/disable the NAS as a Time Machine destination.

If you want the external drive to be the default, remove the NAS from Time Machine or temporarily disconnect the network when backups run.

Hmm, I'm not sure that is 100% correct. In my case, I have TM making backups to three devices: a Synology NAS, an OWC miniStack Max, & a WD My Book Pro. The latter two are directly connected to my 2023 M2 Pro Mac mini running macOS Tahoe.

In this configuration, TM (set with Backup Frequency = Automatically Every Hour), happily runs backups to each of these destinations in rotation. There appears to be no preferences to, whether or not, the destination is a NAS or a locally attached drive.

Usual pattern cycles the TM backups through all available targets, one at a time.

I suspect the sequence is based on updating the oldest accessible backup, and will then rotate through all currently-accessible TM targets.

Put differently, what you are reporting is normal for the standard operation of TM. (Though I don’t try to override the TM default schedule, so TM just does its thing.)

Long-shot:

• is the time on the Mac and on the NAS correct? (Yeah, I know about WWV.)

• Is the firmware on the NAS current?

It sounds like both the NAS and Local drive are backing up properly.

Now go back to the Daily frequency if that is all you need or want and occasional run a manually backup on the local drive after new content or projects are added.

That disk or the path to it looks like it’s corrupt, or malfunctioning.

You can try erasing and recreating it. Probably also run DriveDx for errors.

Given it’s glitching and 1 TB and probably also old, I’d probably replace it larger, and maybe replace the USB path.

I was referring to the disk with the most recent backup from nearly a year ago, and quite possibly failing hourly since. Not to the NAS.

Locally, Time Machine preferably gets the whole target archive disk (and APFS in recent times), and the target archive disk needs to be somewhere between two and three times the total protected storage capacity, and potentially more.

I do not prefer to use local partitioning. On a NAS or other pooled-storage controller, sure. On local storage, partitioning tends to be a way to lose everything when anything glitches, and local USB-connected HDDs and old HDDs tend to glitch. I’ve just seen too many cases of corrupt local partitions, particularly with mixed versions and mixed systems involved.

For more important data and for more complex configurations, preferably also with protected power configured, and with NUT or equivalent where the local gear supports that.

mjcm_nl wrote:

That is not 12th January 2025

01-12-25 = 1st December 2025

I bought this mac Mini in August so how can I have a backup of 12th January 2025.

I never said that the first backup date was January 12 2025.

I only pointed out that it was the date of the first backup.

If it is not what you want..? Double check your Settings > General > Date & Time and Language & Region Settings.

Double check the Frequency settings for the local external drive.

Back up your Mac with Time Machine - Apple Support