Backing up iPhone to external storage (Big Sur)

FWIW, if you are that short of HDD space, you need to offload

a lot more than just iPhone backups. You likely have 100's GB

of files that can be moved to the external drive like photos, movies,

music libraries, etc. which are major culprits in using up disk space.

What system are you running on your old Mac? If you're using iTunes or the Finder (in Big Sur) to manage your iPhone click on Manage Backups, Control (right) - click on the backups you want to delete and select Delete from the contextual menu:

This screen capture is from Big Sur. It's essentially the same in iTunes.

So remove the unwanted backups in the old Mac before migrating to the new one.

I just got an M1 Mac with 256GB drive. On my old Mac I have over 150GB of backups for multiple iPhones and iPads. I would not like to take up almost 3/4 of my available drive space with iPhone/iPad backups. Does anyone know if it possible to send iPhone/iPad back ups to an external drive so I don't have to manually move the files back and forth on and off my Mac every time I want to back up my devices?

Old Mac is running High Sierra with recent iTunes update so my iTunes screen is different than what you have pictured. There is only 1 backup per device verified by going into iTunes preferences, devices and looking at the list of Device backups and also verified by going to the host folder Library>Application Support>MobileSync>Backup. So having a single encrypted full backup for each of my 7 devices (each with 64GB or 128GB capacity) as I stated is almost 150GB. As time goes on the backups will get bigger. If all my devices had half of their memory used the backups would be over 300GB. Thus, I would like the backups to automatically goto my external drive so I don't have to manually move the files back and forth each time I backup my devices.

There is no simple way to accomplish what you want. It is not offered or supported by Apple. You can try, if you are savvy about using Terminal, to create the right type of unix-defined links (which would be like an alias but actually be a link) which might work for a while but could stop working when there is a software update. Backups need to be reliable to create and to restore from.

I think the best choices are to replace your internal SSD with a much larger one, or just use iCloud. You can use iCloud to store all your photos and messages in the cloud for a few dollars per month.

Another option is to download all your iPhone photos to your Mac in a Photos Library or some other storage method, and store that Library on an external drive (not on your Mac's internal drive). Then just keep a subset of photos on your phone. Then you can make backups of that external drive so you always have at least two copies of those images.

Have you tested whether the iOS device backups moved to an external disk can then be moved back to the internal disk and really used as a backup? Does the Mac recognize such moved backup files?

One workaround would be to get an external bootable disk and periodically boot into that to make local backups of iOS devices. That volume could be a minimal macOS install.

Thanks! I was pretty sure it was not supported by Apple but just wanted to make sure there was not an easy workaround I wan't thinking about. You make a great point about the reliability of the backup as it would be more difficult to control and/or verify the quality with so many variables outside the system. I.e. if someone has a drive on the end of a bunch of daisy chained hubs or something like that. I would think it would be easier to control if it was required to be a thunderbolt3 NVMe drive connected directly to the Mac... but then there is the issue of not being able to control the human element connecting it.

I can't install a larger SSD because I have an M1 Mac and no one gave me an extra $200 or $400 for 512GB or 1TB Mac. ;-)

I may start doing iCloud backups and see how big those backups are as they would be smaller than the backups on the Mac. This may work for some of my devices which will then make the amount backed up on the Mac a lot less.

It doesn't make sense to me to offload the data from my devices and have them mostly empty just so I can fit the backups on my Mac.

Thanks! My old Mac mini running High Sierra came with a 512GB HDD and a few years ago as it was showing its age I installed a 256GB SSD and put the HDD as the secondary drive inside the mini. That helped it last a few more years for my purposes. The SSD was the boot drive and my device backups would save to Library>Application Support>MobilSync>Backup and I moved the files to the internal HDD. When I would backup my device I would just move the file for the device I was backing up to the SSD, do the backup and move it back to the HDD. This worked fine and I never had an issue with the integrity of the data. I will definitely test and see if this will also work now that I have an M1 Mac with Big Sur and an external drive.

Good thinking with external bootable disk. Then I can just use that drive solely for my device backups. I will look into this as an option for my needs.

This article may be of help: How to Find iPhone Backup Location and Delete Backups

Thank you. I see in the article the way to change the iTunes backup location. I will experiment to see if this method will work on changing the backup location in Finder on Big Sur also.