Merge two disks to RAID 0 and keep the installation

disk-utilitypartitionraidssd

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

Best Answer

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.

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