How do I partition my MacBook Pro so I can keep Snow Leopard and also install Mountain Lion?

Question

How do I partition my MacBook Pro so I can keep Snow Leopard and also install Mountain Lion?
I want to install the latest OS, but I already know that I will lose a lot of my software unless I can partition the hard drive and have two "bootable" drives.
How do I retain everything I have, partition the drive, then reloa the software I own according to which OS it will work under?

Answer 1

msmedia wrote:
I do not currently own OS X ML.
I am currently running OS X (10.6.8 Snow Leopard) on my MacBook Pro. It has a 2.8GHz Intel Core 2 Duo Processor. I want to upgrade to Mountain Lion, but many of my software titles will not operate with ML and I cannot afford to replace some of them (Adobe Creative Suite, for e.g.)
After I back-up my HD and then partition the HD, how do I use the back-up to reinstall what I want to the SL partition, and then place the rest on the ML partition.
I have not done what you want to do, so can only offer some general thoughts in support. Take value from the following where you can. No guarantees.
If it was me, I would use a disk clone utility (e.g. Carbon Copy Cloner) to image the existing Snow Leopard disk to an external drive. Then verify that the external drive would boot and run Snow Leopard normally.
I would then purchase and download the Mountain Lion upgrade installer, but not run it. Use Lion Diskmaker to make a bootable USB stick, and perform a clean install of Mountain Lion, replacing the Snow Leopard on your MBP. This way, you make absolutely certain that no third-party drivers or other SL cruft remains to make Mountain Lion unstable. Update to latest ML point release. Fix permissions. Let TimeMachine make a full backup of your ML installation to a different external drive. Then turn of Time Machine.
In Disk Utility, use the + sign at the bottom of the ML partition to add another GUID, HFS+ Journaled partition for Snow Leopard. Resize to taste. Name it differently from your ML partition. Exhale.
Now ideally, you would like to reverse the external clone and put it back into the new SL partition. Then fix permissions. And demonstrate that you can boot into individually stable OS X installations. This would save you alot of work. Resist copying your home directory into ML just yet.
If you cannot successfully achieve the preceding paragraph, you will be faced with a full SL and application reinstall.
The ~/Library contents for SL and ML are sufficiently different that you do not want to mix them. You may want to salvage Safari bookmarks.plist. And, ML created folders in the home directory may have different permissions or ACL settings than in SL. So, my rule of thumb would be to copy folders that you created in SL, and only the contents of matching named OS created folders such as Music, Pictures, Downloads, etc.
For each operating system, you probably want the Time Machine settings to exclude the opposite OS X partition. If you use the same host name in Sharing prefs, then you will mix SL and ML backups on the same Time Machine back up drive. If you use different host names, they will be distinct folders in the Time Machine backups.backupdb and allow discrete restores per host. You may also want to gag Spotlight from indexing the opposite OS X partition.