Originally Posted by berrybianka
When I first tried it, it gave me a file not found message. I read the comments and slowly found out how to do the correct command.
I'll try to recreate it. (Sorry can't do screenshots)
1. Copy the backup folder from ~/Library/Application Support/MobileSync/ to your external drive. Put it under a folder like iosbackup so the destination would be like ~/External Drive/iosbackup/backup/
2. Rename the current backup folder to something else like backup1.
3. Open Terminal and type the following command "ln -s" without the quotes. Put a space after the s. Don't press enter yet.
4. Open finder and find the destination which is ~/External Drive/iosbackup/backup/ and drag it to terminal. This will ensure that the address of the directory is correct. Now put a space.
5. Open finder and find the /Library/Application Support/MobileSync/ and drag it to terminal.
6. Next is add "/backup/" without the quotes and press enter.
7. Check the mobilesync folder. There should be a new backup folder there. When you open it, there should be an alias there.
I'm not well versed in terminal or commands and stuff but what I understand is this alias is what is called a symbolic link. Basically, when itunes look for the backup folder, it will find this alias and will be redirected to the folder we created in the external hard disk.
Now to test if it is working. I'm sure you have backups. Open itunes/preference/devices. Your backups should appear here. If not, there is something wrong with the address you put in terminal. You can easily delete the backup folder with the alias and start over.
If in case you change your mind, you can delete the backup folder with the alias and copy the backup folder back to the original location.
Hope my instructions are clear. Do post your questions and I'll try to answer.