As a computer consultant, I often find it useful to be able to boot into different operating systems from the same machine. For example, to help my PowerPC customers, I keep around a laptop that is capable to booting into either Tiger or Snow Leopard as well as Classic.
Up until the release of Lion, creating a multi-boot Mac has been a time-consuming but straightforward process: Make a full backup of the existing system, repartition the drive into two, restore the original OS and install the newer OS into the secondary partition using the Apple install DVD. There’s nothing fancy or mysterious, here.
Lion changes the game entirely. You can’t just create a second partition and begin the Lion install. The Lion installer will invariably greet you with the following error message:
“This disk cannot be used to start up your computer”
You say to yourself, how can that be? My Mac is Intel-powered and meets the minimum system requirements. What’s going on?
The way I got around this perplexing problem was to install a fresh copy of Lion onto an external hard drive, first. Fortunately, I had a used 2.5 inch hard drive available that could be employed for this purpose. I connected the drive to a NewerTech Universal Drive Adapter that I attached to my Mac. Using my Mac’s Ethernet connection, I began the Lion install.
Once installation completed, I restarted my Mac and booted into Lion to make sure the OS was operational. I then rebooted my Mac again with the Option key held down to select and boot into the Lion Recovery Disk Assistant.
In Disk Assistant, I opened Disk Utility. Following instructions outlined on Apple Support Document TS3926, I reduced the size of my Mac’s second partition by 128MB. Afterward, I exited Disk Utility and selected my NewerTech hard drive as my startup disk.
Once my Mac rebooted, I proceeded to clone my 10.7 system from my external hard drive to the laptop using Carbon Copy Cloner. After the cloning process completed, I rebooted my Mac using its internal drive as the startup disk and then installed the Apple software updates (including Mac OS X 10.7.2).