I've got two 128Gb SSDs installed in my MacBook Pro.

Originally I had one for the system (named Calcium), and one for the /Users folder, symlinked into the first (named Users).

As I ran out of space on Users, I shrunk the Calcium partition and created a 50Gb partition named "Swap" on the first SSD, from where I symlinked some folders back into /Users (namely, my iTunes backup and my work folder).

Now I want to get things a little cleaner before preparing my migration to the upcoming Mavericks release. I'd like to setup a RAID 0 with the two drives, keep my ~75Gb Calcium partition (lowering it to 64Gb is OK), and enlarge my Users partition to take the whole remaining space.

I have a spare 500Gb HDD lying around in a FireWire 800 case and a bootable USB stick with the Mountain Lion installer on it, so my plan is:

  1. Using my existing system, copy all data off Swap (about 40Gb) onto a folder of the 500Gb
  2. Boot off the USB installer and start Disk Utility
  3. Create an image of Calcium onto the 500Gb drive using Disk Utility
  4. Create an image of Users onto the 500Gb drive using Disk Utility
  5. Wipe my two drives, create a RAID 0 with them
  6. Re-create a Calcium partition (64Gb is enough) and restore from the image
  7. Re-create a Users partition with the remaining 192Gb
  8. Restore Users from the (smaller, 128Gb) image
  9. Reboot the system from Calcium
  10. Transfer data that previously was on Swap (not needed to boot) directly to the new, larger, Users.

According to that other similar question I believe that should work, and my existing system won't be confused when being restored.

My questions :

  • do you confirm I won't run into problems with this process? No data loss, no boot problems, no confused OS?
  • what image format should I use when imaging the partitions at steps 3-4 using Disk Utility? The default read/write format produces a DMG that's fully restorable
  • can I backup a 75Gb partition on a 64Gb image (for Calcium) if it has less used space than total space on the original partition? yes I can, in fact it's the default behavior of Disk Utility when you backup a partition
  • similarly, can I restore a 128Gb image on a 192Gb partition (for expanding Users)? yes I can
  • If you don't get a good answer, let's open a thread on Ask Different Meta to discuss how to improve multi part questions on the site. My guess is with all the questions at the end this will get voted as too broad and/or just ignored by people that have a good answer for one of your questions but can't address the other 4 (or 5)
    – bmike
    Commented Aug 6, 2013 at 10:20
  • Actually I have made some progress myself, I'll edit my post.
    – Cyrille
    Commented Aug 6, 2013 at 10:46
  • Perfect. One thing I've done is isolate each sub question and get the answer, then ask one overall "jeopardy style question" where you ask the combined question and answer it yourself.
    – bmike
    Commented Aug 6, 2013 at 11:02
  • Well, that's what I'm trying to do in my spare time. So far I have tested creating and restoring images, this weekend I'll take a deeper breath and try restoring a bootable partition on another spare drive formatted as RAID. If all goes well, I'm gonna take the deep plunge and perform the whole process on my production system, and will answer myself if nobody has answered until then.
    – Cyrille
    Commented Aug 6, 2013 at 11:49

1 Answer 1


Just use Time Machine.
Backup the whole laptop, reinstall like you want and then restore or import using the migration assistant in the utility folder on you mac.

  • I can't "reinstall like I want", my IT department needs some setup that I'd rather not touch. I have the right to move around hard drives, etc, but there's an admin account whose password I don't know and that must be kept. The whole purpose of my question is if it's possible to re-architecture my partition map while leaving the underlying installation intact.
    – Cyrille
    Commented Aug 5, 2013 at 9:53
  • Both Time Machine and making bootable images have benefits and drawbacks. I'm seeing less and less problems with apps not expecting Time Machine so although you might see this answer as a diversion - for most people, it actually is the best answer. Once you are free to erase things, you know you have a good backup and you have much less steps to set up your new setup using stock tools.
    – bmike
    Commented Aug 6, 2013 at 10:17

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