Issues using an external drive for TimeMachine

The improper ejection error, Finder beachballing, and hard system crashes you are experiencing suggest that your Kingston M.2 SSD is experiencing hardware-level disconnections while macOS is trying to write data. When a Time Machine drive drops offline mid-transfer, it severely corrupts the backup filesystem, which causes Finder to completely freeze when trying to mount or read it. This behavior points to a reported hardware quirk involving the rear Thunderbolt/USB-C ports on the M4 Mac mini, combined with high-performance M.2 NVMe enclosures. 

The other possibility is that your internal drive is getting full, but that would typically generate a disk full error. Still worth checking free space on the Mini to rule that out.

Here is the prioritized troubleshooting approach to isolate the power/connectivity issue and fix the corrupted Time Machine volume.

1: Isolate the Hardware Flaw (Power & Cables)

M.2 NVMe SSDs pull substantial peak power during Time Machine write cycles. Many users on the Apple Insider and MacRumors forums have noted that the rear ports on the M4 Mac mini can intermittently cut power or drop connections during heavy I/O tasks. 

• Move the drive to a front port: Swap the SSD to one of the front USB-C ports. The front ports run on a slightly different controller configuration and have resolved unexpected drops for multiple M4 mini users.
• Change the cable: M.2 enclosures are highly sensitive to cable quality. Ensure you are using a high-quality, short Thunderbolt 4 / 40Gbps certified cable rather than a standard USB-C charging cable.
• Use a powered USB-Hub: If the enclosure lacks external power, try connecting the drive via a powered USB-C/Thunderbolt hub mitigates power starvation issues under load.

2: Unstick Finder and Mount the Drive

Because Finder is beachballing, it is stuck in a loop trying to verify the corrupted volume. You need to force it to let go before you can fix it.

• Unplug the Kingston SSD from your Mac mini.
• Press Option + Command + Esc, select Finder, and click Relaunch to clear the beachball.
• Plug the SSD into a front port. If Finder beachballs again, do not click on the drive. Proceed immediately to Step 3. 

3: Repair the Damaged File System

Because the drive disconnected mid-backup, its APFS file system contains errors preventing Time Machine from completing.

• Open Disk Utility (via Spotlight or Applications > Utilities).
• Click View in the top-left corner and select Show All Devices.
• Select your Kingston SSD from the list (pick the parent device name, not just the volume underneath).
• Click First Aid at the top, then click Run.

Note: If Disk Utility freezes or fails to complete First Aid, the file system container is completely corrupted by the hard shutdowns. You will need to click Erase in Disk Utility to reformat the drive as APFS and start a fresh Time Machine backup history.

4: Adjust macOS Sleep Settings

To stop the operating system from severing the data connection when the Mac goes into a low-power state:

• Navigate to System Settings > Energy Saver (or Displays depending on your exact macOS configuration).
• Turn off "Put hard disks to sleep when possible".
• Enable "Prevent automatic sleeping when the display is off

More info from Apple:

If you can't back up or restore your Mac using Time Machine - Apple Support

Time Machine troubleshooting on Mac - Apple Support

If Time Machine on your Mac can’t find your backup disk - Apple Support

Personally, my primary backup for four Macs in the house is a local Synology NAS and secondary backups are to a pair of large SSDs (that I swap offsite weekly), and all are working reliably.

Here's what solved it for me. As a human I would also ask why Apple/TM does not have some better messaging as to what may be causing issues - issues do happen. Instead they offer a progress bar that may or not appear depending on how deep in hole you are. I followed all advice on every message board I could find (i.e. reboot, upgrade, first aid, vpn off, no vm backups, good cable, 9 month old 5TB Lacie from Apple, MacBook Pro, 14-inch, Nov 2024 Chip: Apple M4 Pro, memory: 24 GB, macOS: 26.7.2 , Storage: 341GB of 494GB used - this is the step that fixed in my case.

Manually delete Time Machine local snapshots

• Click Skip/quite TM backup if one is running and taking forever.

Open Terminal.

• Enter the command tmutil listlocalsnapshots /
• Press enter. This will bring up a list of all snapshots on the disk, date and time-stamped.
• For each snapshot older than 24 hours*, enter the command sudo tmutil deletelocalsnapshots followed by the date and timestamp. For example, sudo tmutil deletelocalsnapshots 2021-06-26-123740

*in my case I ended up deleting all

Depending upon the size of the current backup, that Found .... changes may take what seems like forever before a backup actually begins. You should be excluding any Virtual Machine guest stored on your Mac hard drive too. Any change within it triggers as a change event that Time Machine will then back up ever so slowly…

Its about patience… This is more painful with a 5400 rpm rotational drive (that may be failing) than the USB-C 3.2 Gen 2 rated external SSDs that I use for TM backup. I have had TM backups fail when I was using rotational drives, but never with SSDs since 2020.

I agree with neuroanatomist's view point about your setup or the need to boot into Recovery and run Disk Utility First Aid on that TM drive. You cannot assume that Time Machine will delete whatever it has to to accommdate the size of your current backup. It only deletes what it has scheduled to delete and that may fall short of the current backup storage requirement — leading to failure.

Thank you for pointing out that I can delete snapshots with Disk Utility rather than via terminal and command line. As mentioned I successfully backed up on 11/02/2026. As mentioned I have MacBook, point being I disconnect (yes, properly eject) my backup drive. On 11/06/2026 I returned to my desk, plugged in TM clicked Backup Now and walked away. I did not return for 24 hours saw that Backup Failed... but no reason given. I clicked Backup Now again and when about my day. I return on 11/08 and see it failed again. I used the Disk Utility method and saw several local snapshots. One was from 11/01 - the day before my successful 11/02 backup, as well as local snapshots from 11/06 and one 11/08. I used Disk Utility to delete those three local snap shots then clicked Backup Now... and Success. My hypothesis - something about these local snapshots is interfering with TM backup process itself. Anyone have any thoughts on this?

I've heard everything from no issues with Time Machine to many posts like this stating that TM is painfully slow or not working at all. I am once again working for days trying to get TM to backup. I've heard theories about which ports not to use and to turn VPN off ,etc. I've done it all. Backed up 3 times successfully in 2 years. Stuck on "Found xxx,xxx changes...", MacBook Pro, 4-inch, Nov 2024, Tahoe 26.6.2

Peter DiSalvo wrote:

Backed up 3 times successfully in 2 years. Stuck on "Found xxx,xxx changes..."

For most of the past two years, there were 5 Macs in my house though that dropped to 4 when my oldest started college this fall. Hourly backups from 4-5 Macs plus weekly backups to a pair of SSDs means tens of thousands of incremental backups in 2 years, from Macs running Sonoma, Sequoia, Tahoe and now Golden Gate.

The issue is with your setup, not with macOS or Time Machine.

Glad that fixed it for you. Note that you can delete TM snapshots easily via Disk Utility – select the top-level volume of your internal drive (Macintosh HD unless you’ve renamed it, as I have), then View menu > Show APFS Snapshots (some explanations of the information shown can be found at this link), select one or more snapshots then click the (–) button at the bottom.

Also note having snapshots older than 24 hours is not necessarily a problem. Snapshots are saved for 24 hours, but also the last snapshot for each backup destination is saved, regardless of age. My backup strategy is hourly to a local NAS and periodic backups to a pair of SSDs that I swap offsite (to my office, where I usually go once a week but skip some weeks). Thus, the backups from 20-October and 27-October are the latest backups to each SSD. They are not problematic, TM is working just fine for me.

So far I have no Problem with Time Machine Back-up with AFP just today Mac OS 26.7.2 with Synology 124.(USB Disk) Before with Airport Extreme last Generation (USB Disk) it was always working for years with different macOS

never had problems with time machine and external hd's