Ok, I thought I would document and share the steps I took to install Mojave onto a RAID0 dual SSD setup that is bootable with APFS as the drive system. Some of you may be aware that the latest MacOS no longer supports booting from a RAID setup with APFS.
I give acknowledgement to the following two sources that I used to have success - mine is a variation of both:
This specific post on MacRumors: Mojave on RAID with APFS - a HOWTO | MacRumors Forums
This post from the Apple Developer Forums: https://forums.developer.apple.com/thread/108321
Okay, here we go.
What we need:
- Latest version of Carbon Copy Cloner (CCC) that can back up APFS in bootable form.
- Two SSDs of similar sizes to create the RAID0 single virtual drive.
- An external drive to clone your boot drive to.
- About 2-3 hours of time and lots of patience.
Step 1: Clone your OS boot drive from internal to external
Make sure your boot drive is updated to the latest version of Mojave.
Use CCC to clone a bootable copy of your OS drive to the external drive.
To be safe, reboot holding down the left OPTION key, select the external drive, to confirm it can be booted and is working.
Step 2: Create the RAID0 drive
Repeat, make sure both SSD drives have been backed up - this process will erase all data on them.
Open up Terminal
Enter this command:
Find out the unique identifiers of each of your SSDs - they are their identifiers, and should be like disk2s2 and disk3s2 or something like that. Make sure you have the right drive identifiers!
Once you are sure, enter this command to create the RAID0 array (use the correct drive identifiers below):
Diskutil appleRAID create stripe NameOfYourNewDrive APFS disk2s2 disk3s2
- Wait until this process finishes.
Step 3: Clone the OS boot drive from external back to internal
- Like Step 1 but in reverse - use CCC to clone the OS drive you backed up onto the newly created RAID0 volume.
Step 4: Boot up your new Mojave OS on RAID0 - you have to do this each time you restart.
While rebooting, hold down COMMAND-S to boot in Single User Mode.
Wait for all the text to scroll pass - once the command prompt for ROOT shows up (you may have to hit enter if you can’t see it), enter the following commands, pressing enter after each line:
/sbin/mount -uw /
- The system will then boot up into Mojave successfully.
The advantages is that you are now running the latest MacOS on APFS on a RAID0, so you get speed.
The disadvantages are significant:
- You have to go into Single User Mode as per Step 4 above each time you restart
- You cannot update the system easily - to update, you need to do so via a cloned drive - clone the drive to an external bootable clone with CCC, boot into that drive, update it, and then clone that drive back to the internal RAID volume.
- This last disadvantage is a general risk for running a striped RAID0 array - you have faster speeds, but you trade that for greater risk of failure - there is no redundancy, so if one drive fails, the whole system fails, so make sure you have backups.
Hope this helps someone out there. Took me a couple of tries to work it all out.