I've downloaded Mac OS X Mountain Lion today and wanted to backup the installation image to a USB drive for later.

I've created a new empty partition of at least 8 GB size on the external drive using *Disk Utility*, and tried to restore the *InstallESD.dmg* image to this new partition, via the *Restore* menu.

However, doing that, I get the following error message, right after it finishes copying:

> 
> Cannot Allocate Memory
> 
> 
> 

What can I do now?