How much space does an iOS backup require?

seahorsemonkey wrote:

I'm trying to backup my iPhone 6s, on my Pro Book.

I have around 10GB of free space, on my Book, than the storage on the iPhone is using.

Still, "there is not enough space" ...

How much 'extra' space do I need to be able to do a backup, really?

I tried a tip with making itunes backup on an external hard drive. It didn't work.

It all depends on how many backups you have previously done, and what is included in the backup. This tip describes what is included: About backups in iCloud and iTunes - Apple Support. If you have a lot of photos and don't use iCloud Photos then the backup will include all of the photos. Other than that, backups will be relatively small, as they will only contain system settings and app data.

You can clean out old backups to make more space. Open iTunes Preferences, Devices page. There will be a list of previous backups. You can select and delete any you don't need.

It is possible to move your iTunes backups to an external drive. Either the tip you saw was not correct, or you didn't follow the instructions exactly. Do you have Windows PC or a Mac?

Hi there, seahorsemonkey!
Thanks for reaching out to the Apple Support Communities! It sounds like you are having an issue backing up your iPhone to your computer and I am happy to help out! Thank a look at this article with the best steps to follow If your iTunes backup couldn't be completed or you can't restore from a backup. This will give you the best steps to try as well as what to do if your issue is not resolved after trying the steps.
Take care!

seahorsemonkey wrote:

Don't a new backup overwrite the old one?

So I basically will only have one backup at any given time, no??

Yes and no. Backups are incremental, meaning that when you do a backup it only copies information that has changed. So in that sense there is only one backup, and it will appear that the new is overwriting the old, although technically it is supplementing it.

However, as you have a Mac, you can archive a backup. If you do the next time you make a backup it will be completely new, and will not overwrite the old. Open iTunes Preferences, Devices panel. Right click on a backup and you will see an Archive option. Select it and that backup will then not be overwritten.

To move your backup to an external drive, this is a good explanation: http://osxdaily.com/2016/03/04/backup-iphone-to-external-hard-drive-mac/

What you do in summary is:

1. Launch Terminal
2. Create a folder to hold backups on the external drive using Finder
3. Copy the current backup folder contents to this new folder (the current backup folder is ~/Library/Application Support/MobileSync/backup)
4. Rename the current backup folder to backup.bak (just to be safe)
5. Using Terminal, add a symbolic link from the current location to the folder you created on the external drive; an example of that command is:
   ln -s /Volumes/FileStorage/iTunesExternalBackupSymLink/Backup/ ~/Library/Application\ Support/MobileSync
6. Step 5. is the only tricky part. That command must be all on one line, the spaces need to be in the same place, and you must change the folder name on the external drive to the drive name (here FileStorage) and folder name (here iTunesExternalBackupSymLink) that you created.