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Why won't Time Machine overwrite/delete files to make room for new backups?

I can't imagine your average user has a 10TB hard drive. So when I have a 500GB HDD and 'only' a 1TB external HDD for backups, it would make sense for Time Machine to recognise that and help me out by not expecting to be able to make multiple COMPLETE backups of my system to a drive that could only fit 2 x full backups on it, but rather incrementally back up files that have changed.


So to my question: when trying to back up my 500GB system to a 1TB external drive, why is Time Machine refusing telling me "There isn't enough space on TimeMachine" instead of doing what it purports to do by deleting the oldest backup to MAKE space?? Do I really have to manually delete my entire backup and then perform the entire backup again? That doesn't seem very "it just works". Or did that mantra die out with Steve??

MacBook Pro 13", macOS 10.13

Posted on Jun 4, 2019 2:33 PM

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Posted on Jun 4, 2019 3:57 PM

If it finds there is something wrong with a backup, it will start another full backup.


You may need to reset Time Machine fully and erase the disk in order to get it to work correctly.

Or, the drive may be corrupting the backup and is unreliable.

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11 replies

Jun 4, 2019 4:04 PM in response to Barney-15E

No, it doesn’t seem like it’s finding anything “wrong” with the backup, it just says there’s not enough free space to back up, which is understandable because most of my backup drive was taken up with the last back up… But what it should be doing is deleting files that have changed since that back up and over writing them with new a file so that I can always have at least one good full back up that time machine takes charge of. No?

Jun 4, 2019 4:14 PM in response to BDAqua

MThanks, yes it did seem to me this was probably how it operated, however badly designed this may be…! Again, Apple seems to assume if people can afford a $1000 computer then they can probably also afford a $500 external hard drive back up station with endless terabytes of storage…! I guess the best option for me is probably just to forget Time Machine even exists and set a reminder to manually back up every few weeks. Sigh, Apple.....

Jun 4, 2019 4:50 PM in response to peanutismint

Time Machine is designed to work as you want it to. A full backup is only going not take the amount of used space on your hard drive, which is hopefully much less than 500 GB. Unless your hard drive were completely full, then you should be able to store quite a few incremental backups. My guesstimate would be at least six months of backups before any older backups would need to be deleted.


There must be some other problem with either your machine, your external drive, or your system configuration.

Jun 5, 2019 5:19 AM in response to peanutismint

If this is a Time Machine backup for your Macbook Pro, then my experience is that if the Macbook Pro is disconnected from the back device (whether physically attached or over a network to a Time Capsule or similar Network Attached Storage (NAS) device), it is possible to one day disconnect at just the right moment, and corrupt the Time Machine backup.


If you NEVER disconnect the backup device, that is less of an issue. For example, I have 2 Macs that are stationary, and always connected to their backup devices, and Time Machine works great. But my Macbook Pro systems I've stopped using Time Machine, and depend on Carbon Copy Cloner or SuperDuper (although these days is is mostly CCC).


The nice thing for me about Carbon Copy Cloner is that it can do a network backup to another Mac acting as the backup server attached to lots of disk storage. And CCC can also aromatically mount a network drive (in my case a Synology, but it can be any network drive), and then it mounts a macOS disk image so that I am backing up from a Mac file system to a Mac file system, even though the storage device in my case is a Synology NAS running Linux, using a Linux file system.


Anyway, look at how you handle your Macbook and your backup drive. If they are not always connected, consider a different backup utility.

Why won't Time Machine overwrite/delete files to make room for new backups?

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