Dear Aunt TUAW: How do I install a Lion partition on my MacBook Air?

Dear Aunt TUAW,

I'm in the Mac Developer program and I'd really like to be able to install Lion on my MacBook Air as a second OS. What are the best strategies to do this? Is it worth going out and buying a second SSD drive and swapping that out with my primary Snow Leopard system?

Thanks for letting me know!

Love and Kisses,

Your nephew G

Dear G,

Auntie turned to one of our former blogging staff to see if your swap-the-SSD approach was doable. Apple repair expert Josh Carr advised against. "You're talking about the new MBA with the blade SSD," he said. "Swapping the drives out isn't hard, just dangerous -- static could kill the SSD. It would require a screw driver and a second unit for the second OS. There are a lot of places selling the blade drives now, but it seems like it wouldn't be worth the effort. The older style SSDs would be even more difficult."

Instead, Josh advises that you just partition your drive. Although the drive size is small, you only need 10-20GB to get a good test environment set up for Lion. Plus, there are a number of simple ways you can set up your preferences to share your home and applications between both partitions.

First, you'll want to partition your drive. Disk Utility allows in-place partitioning if your drive is not particularly fragmented. Before doing anything, back up your drive and verify your backup.

Then launch Disk Utility, click your main drive, click partion, click +, adjust the size of your partitions, and click Apply. Disk Utility should confirm that it will be able to do the in-place partion without erasing. If it does not, do not click Apply. You may need to use a third party tool instead.

You'll probably also want to run Software Update before doing any installations, to bring your system up to date and avoid any dangling prerequisite updates that might snag you during the install process. Repairing your disk is also a good preparation step.

You're now ready to install the new OS. When doing so, be sure to select the correct partition -- a little oversight that came to bite one of our TUAW family yesterday.

If you're doing any kind of OS X install from a thumb drive, don't forget: make sure your drive is partitioned using GUID and formatted with HFS+. As with any OS X install, you can use Disk Utility to restore an install image to that USB drive and then use Startup Disk to select that drive.

Once you've installed Lion, you can take advantage of several standard OS setup features to allow you to better share your computer between two operating systems. Here are two suggestions courtesy of Uncle TJ Luoma.

First, you can take advantage of the advanced options in System Preferences > Accounts to redirect an account's home folder. Right-click the account name to access those Advanced Settings and then edit the "Home directory:" field (there's an interactive Choose... to simplify selection) so both partitions share the same home folder on the larger disk segment of your system. Once set, you will need to restart your computer.

Second, you can share applications by linking your Snow Leopard /Applications folder to the home folder ~/Applications directory used by Lion.

Obviously, when performing these tricks, try to avoid renaming or otherwise fussing with your partitions after setting up your links.

Best of luck with your new OS install!

Hugs and kisses,

Auntie T.