Why does Time Machine keep failing after initial backup on Mac?

ThirtyTenDesigns wrote:

Time Machine has been working great for many years using a 12TB Western Digital external hard drive connected to a OWC hub to my MacBook Pro M2 Max. About two weeks ago, I started getting an error every hour saying "Time Machine couldn’t complete the backup to “Time Machine 12TB" An error occurred while preparing the backup.".

So got a new 8TB Western Digital drive and connected it the same way, did the initial backup and it worked for about 1 week, then I started getting the same error message with this drive. Erased the 8TB drive yesterday and started the initial Time Machine backup again and completed it without issues.

Now again, after that initial backup, I'm getting the same error messages.

Any ideas on how to get Time Machine working again? I do also backup online to Backblaze, so not extremely concerned, but would like to know what this keep happening.

[Re-Titled by Moderator]

I have never been a fan of Western Digital if that is the issue...

Have you erased/reformatted/initialized those drives as new to remove any proprietary software that comes preinstalled on WD — this has been a known issue.

Don't pay more for a drive that says Mac ready or some such advertising(?)

Erase and reformat a storage device in Disk Utility on Mac

Erase and reformat a storage device in Disk Utility on Mac - Apple Support

TM likes to have dedicated drive, not shared with Containers/Partitions/ other volumes with user data...

I can say this is one of the classic error messages when a drive is working in a state of failure:

Time Machine has completed a new backup for you

can't create the backup

failed to complete the backup

an error occurred while preparing the backup

If you continue to get these errors I would suspect the Time Machine drive is starting to fail, the answer would be replace the drive and /or try another drive and compare your results..

Time Machine troubleshooting on Mac

Time Machine troubleshooting on Mac - Apple Support

I'm having a similar issue that apparently appeared with Sequoia 15.3 or possibly 15.3.1. Working with a new (since late december) 4TB Crucial X9 Pro SSD. I reformatted it as APFS/GUID after purchase and used it exclusively as a Time Machine backup to an M1 MacBook Pro 1TB. Seemed to work well until early February when it refused to mount suddenly, and Disk Utility reported unrepairable errors, suggesting backing up ASAP. I reformatted it and tried again, and while it didn't again fail to mount, after a few daily TM backups, DFA was again reporting unrepairable errors. I called Micron and the tech claimed they'd seen reports of similar issues with various drive manufacturers under 15.3 and recommended formatting with exFAT or HFS+. I tried both, with the same errors cropping up after only a couple of backups. I'm deciding it must be a bad drive or a 15.3 vs. Time Machine issue... Will be talking to Crucial/Micron on Monday. May be worth a call to Apple support too.

Exact same behavior here. Also using an external USB C connected WD 12 TB drive with a TM partition sized way larger than months worth of backups from my 1TB internal drive.

Erase/format/initialize disk, run first Tm backup and it works fine to backup the whole disk. TM is set to do daily backups and it runs fine for some random number of days, then all of a sudden starts failing with errors about different files being inaccessible to TM. After the, even if the offending file is removed or the containing folder excluded (as a troubleshooting measure), TM never backs up completely again. Only way to recover is to blow away the TM disk and start again from zero.

This only started with OSX 15.

Well, I redid the drive again, wiped out, formatted, start daily TM backups.

Worked for two days, one "full" initial backup, the following daily and then it's dying again. No backup for the past two days. Failed again with a familiar pattern:

Time Machine couldn’t complete the backup to “Time Machine”

“/Users/jp/Library/Mobile Documents/com~apple~CloudDocs/Techstream_Setup_V15.00.026.exe” could not be backed up.

Funny though, it could be backed up with the initial one, and when I search for that file, it's on the drive same place it's been forever? This is also *not* the same file that it's failed on before, and all the previous times it's been some other random file causing the error.

The mystery continues....

Were you able to figure this out? I'm in a similar boat with the X9 Pro, suddenly not mounting (greyed out in Disk Utility), fails First Aid check.

Did Micron/Crucial give you any more information, or Apple? Thanks in advance!

BTDROSS- have you contacted Micron or Apple about this specific issue? If so, I’d love to hear what they had to say… my Crucial replacement drive is scheduled to arrive tomorrow (direct from Malaysia…). Naturally I’m gone for a week beginning this afternoon 🫤

I've called Micron, spoken with customer support. I tried to leave the drive connected overnight for the indexing, though that didn't change anything. They asked me to send SN, proof of purchase, etc. which I did 5 days ago but still haven't received RMA number or address to send to.

Good luck with your replacement - let me know what you discover!

Btdross, in my experience it was helpful to do online chats with support and mention that you’re still waiting for things. Support IS outsourced to an overseas location, and I found verbal chats challenging.My replacement arrived a day earlier than scheduled! I had time to set it up as a Time Machine drive and do an initial backup before being away from my laptop for a week. It’ll be a while before I can report on any success… or otherwise.

Reply to btdross…

Micron eventually gave me an RMA to return the drive. Still waiting for a replacement… Here's hoping this IS a solution to the problem, but I’m not holding my breath…