Time Machine full, cannot add new computer to backups

I have a new MacBook Pro I want to start backing up to my Time Machine.

The Time Machine doesn't have enough space. When my older computers use up space on the Time Machine, I get a message saying old backups are about to be deleted. I click OK and things proceed as normal.

How can I allow the new computer to also delete older backups, as necessary, so I can start regular backups from that computer?

Brad BansnerWeb DeveloperAsked:
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If your time machine is a TimeCapsule, the easiest thing to do is to attach a large USB drive to the TimeCapsule and back up to the USB drive through the TimeCapsule.

The USB drive has to be formatted as AppleExtended Format (Journalled) using Disk Utility.
Brad BansnerWeb DeveloperAuthor Commented:
I would have to acquire a hard drive to do that. Can't I somehow just tell the Time Capsule "I have a new computer, please make space for it"? I'm able to do that when its an existing computer backing up and there is no space.
It is not impossible, but it is difficult and involves terminal commands and you run the risk of doing damage.

It is also probably not a good idea to back up three Macs to one time capsule. How big a drive does your time capsule have? How much data is on the three Macs. You typically need twice the hard drive space for a backup as for the original data as you will want to keep not only a complete backup of the current drive, but historical data as well.

Add up the amount of data on your three Macs and double it. Unless that is less than the size of your TimeCapsule drive, backing up all three Macs to one TC drive is not likely to work.

You can probably buy an external 1 TB USB 3 drive for under $60. That will give you more storage and save you a whole lot of time and aggravation.

Your other alternative is to erase the existing TC drive and make fresh backups of all three Macs, but that will lose all your historical data and take a few days. Is your time worth $60?
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Justin BradshawOwnerCommented:
You just need to find out what is on the drive and whether you mind deleting it or not to make space for the backup you want to perform.

You should see the Time Capsule in the sidebar of the finder and clicking on it will allow you to load up the drive to see what's on it. It will likely have a few files that say .sparsebundle at the end. Those are backups of other Macs (or an older OS version of yours). You can choose File > Get Info on them to find out how much space they are individually taking up and you can look at the bottom of the window to find out how much space you truly have available on that drive. (or just find the Time Capsule drive on the desktop and click File > Get Info there)

Then you can make a decision about keeping old backups or deleting them... and whether you'll have enough space to backup there if you remove something.

There are a lot of variables here and it's hard to predict everything you'll see, but these are the basics of it. I help clients do this all the time because while Time Machine is good at getting rid of old backups for a computer that is currently backing up... if you get a new computer or have multiples, then it won't delete a backup for another computer to make space for you current one. That would be a bad policy because it could erase someone's backup that they really wanted or needed!

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David AndersTechnician Commented:
Although James Pond died, his site is still active and is considered one of the best Time Machine resources on the internet.

You can screw with TM backups (risking damage), but erasing everything and starting over is the cheap approach. Larger backup device is the smart thing to do.
Brad BansnerWeb DeveloperAuthor Commented:
Thank you for all the help!
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