Increasing size of Time Machine storage partition

Question

I have a 500GB hard drive attached to my iMac. When it was first attached a friend partitioned it equally for storage and backup (Time Machine). Now the backup part is full but the storage is hardly being used.

I'd like to increase the proportion of the drive dedicated to backup but when I click on this part it says 'This partition can't be modified.' There's no problem resizing the storage part though.

How do I increase the size of the Time Machine backup target partition?

It's on an external hard disk, in case that makes a difference.

Answer 1

Your problem is coming from the fact that your Time Machine partition is the first one on your external drive. And Disk Utility can't resize the first partition of any disk.

The only way to workaround this impossibility is to use another external disk and partition it as this ( you can use a temporary one, but in this case you will have to make the migtration operation twice ):

1. Dummy volume the smallest as possible, which will avoid this problem now and forever: dummy ( you will never use it and never need to resize it ).
2. A new large volume for your Time Machine: Backup.
3. A third one for your Data: Work.

Then you will have to use Disk Utility, unmount your 2 sources volumes, and use the Restore function to restore your 2 newly created volumes from your actual ones (this is not a real restore but a copy, but the user interface of Disk Utility is stupid and dangerous).

When unmounting the sources volumes, you enable Disk Utility to make block copies of complete file-systems which will be much faster than copies at the file level.