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Time Machine Back Up Error

I've seen some old threads on this but they are several years old. I have a new-this-year Mac Air M2 running Ventura. Time Machine was working fine on my external HD but now I keep getting an error without saying what it is. Last week it said my HD was full (computer one I assumed) but I deleted stuff and it seemed to back up once. Now I'm getting this annoying error again." An error occurred while preparing the backup".

When I go into Time Machine and try and erase old back ups (which happened automatically on my old Intel Desktop) I'm unable to. I'm thinking I'm going to have to do something drastic and erase all my backups and begin again (once I've updated all the important stuff on USB sticks). But I'd rather it would just delete old back ups automatically.

Thanks in advance.

MacBook Air, macOS 13.2

Posted on Oct 25, 2024 7:14 AM

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Posted on Oct 25, 2024 2:42 PM

Just a quick warning: backing up items from your documents folder with a USB stick is better than nothing but so much of our data isn’t in the documents folder. Photos, music & video, and preferences data are elsewhere and depending on your collection may not fit on a single USB stick. The situation you find yourself in is one of the reasons I use a multi drive drive backup system. With two drives used for backups if one of them dies or the backup becomes damaged I still have a backup. Actually I still have 2 because I use 3 drives and one is always out of the house in case of fire or other disaster.

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Question marked as Top-ranking reply

Oct 25, 2024 2:42 PM in response to Bubbity

Just a quick warning: backing up items from your documents folder with a USB stick is better than nothing but so much of our data isn’t in the documents folder. Photos, music & video, and preferences data are elsewhere and depending on your collection may not fit on a single USB stick. The situation you find yourself in is one of the reasons I use a multi drive drive backup system. With two drives used for backups if one of them dies or the backup becomes damaged I still have a backup. Actually I still have 2 because I use 3 drives and one is always out of the house in case of fire or other disaster.

Oct 25, 2024 11:51 AM in response to Bubbity

The exact wording of that message is important. If the source is named "Macintosh HD" and the message states Time Machine could not back up the disk named "Macintosh HD..." it is referring to the source volume. Read this Discussion for an illustrated example: Time Machine unable to complete backup - Apple Community


"An error occurred while preparing the backup".


That on the other hand can refer to a number of different causes. If there is no other obvious cause or likely explanation I'd erase the backup drive and start a new set. Obviously you wouldn't want to do that unless you created at least one additional backup on separate drive first.

Oct 25, 2024 9:23 AM in response to Bubbity

If TimeMachine tells you the hard drive is full it is referring to the backup drive. When it can, TM will delete old backups to make space for a new backup but TM will never delete files that are part of a complete backup so sometimes TM cannot clean up enough space for a new backup set. This is why most of us recommend a TM backup drive be at least twice the size of your computer’s hard drive. This gives you plenty of room to spare. In cases where a backup cannot be made because TM is unable to clean up space you have two choices: erase the drive and start over or purchase a new backup drive. Personally, I’d never erase my only backup so I’d buy a new drive.

Oct 25, 2024 11:23 AM in response to dwb

Thanks. But my external HD is 2 X TB and I think last time I looked there was plenty of space (on iPad just now). I don't understand either why when I enter TM and go to older backups there's no option to 'delete'. I think there used to be. I can go back in TM but only the 'cancel' button is active (the restore one is there but greyed out) so I'm wondering if there's a glitch. I probably will end up investing in a new one but don't want to shell out and still get the same problem though!

Oct 25, 2024 12:21 PM in response to John Galt

Thanks. Yes I got that message last a week or so ago and worked out it was the Mac HD, cleared some space and then back up took place the once. But now when it won't complete the back up it it just tells me there's an error. I think though there may have been an error code, so maybe that will help? But yes, I wouldn't be happy about erasing the drive either.

Oct 26, 2024 2:32 AM in response to dwb

Thanks dwb. Yes although I've not maintained my photos/videos onto USB sticks as regularly as I was (although the newer ones are on iPad and iPhone aren't syncing with the Laptop but that's for another time!) I have been got years' worth on USB sticks which hold a lot. I got a several as older ones kept filling up. It's mainly the photos and documents. I totally get keeping a spare one somewhere else. Something I used to do!

Oct 26, 2024 7:49 AM in response to Bubbity

Just to update today. I had a vague memory from the last backup that TM worked after I restarted the computer . I tried this again today and lo and behold it worked again! I'm not sure why this is happening as I've never needed to restart before TM backups. A bit tedious, but if it works each time, I'll do it. Thanks for all your input and if any of you can any shed light on this glitch that'd be welcome too.

Oct 26, 2024 10:27 AM in response to Bubbity

It should certainly not be necessary to reboot for TM to resume its activity. Perhaps the drive is becoming unmounted for some reason. Try ejecting the drive, then disconnect it from the Mac and reconnect it again. If you are prompted for a password, provide it and select "remember this password in Keychain" or words to that effect.


This is just a guess.

Time Machine Back Up Error

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