I recently upgraded my Mac Mini Server's dual SSDs and found myself needing to re-create the RAID-0 array from scratch. (I am running the mainline High Sierra 10.13.1 on a 6,2 MacMiniServer from 2012.) I did this from the command line and formatted the filesystem as APFS. The command

diskutil appleRAID create stripe RAID APFS disk0 disk1

executed without a hitch and I found myself with an apparently fully working dual SSD APFS RAID-0 array. I later used Carbon Copy Cloner 5 to repopulate the drive with my the system's contents, and the operation proceeded without a hitch.

Alas, when push came to shove, I found myself with the cryptic error message

Error loading kernel module cache 0x7

being repeated endlessly on the screen. (Fortunately I had the presence of mind of setting booting in verbose mode before undertaking this operation, I don't know whether this would have been visibile in an ordinary configuration.)

There wasn't even a bootable Recovery Partition available. I had to boot into Internet Recovery Mode, which despite its ancient appearance was somewhat helpful: Disk Utility saw the individual drives and their slices, and the RAID array that was spanning them, and reported it as healthy and populated. Unfortunately the Time Machine Recovery client didn't report the drive as being a legitimate target for restoring to.

Apple support was no help at all. The excellent folks at Bombich Software (makers of Carbon Copy Cloner) were much more helpful, despite it being their Thanksgiving holiday.

Meanwhile I literally had to leave the country to resume working at another branch office with a working system because I have an urgent project to complete (I never anticipated rebuilding the machine would take more than a day).

I have now resolved that when I get back to my stricken machine I'll reformat the array as HFS+ and re-image onto that. Quite probably that will work (essentially the same exact situation I was in before I began this, albeit with much bigger SSDs).

Long story short: APFS on RAID looks like it should work, and some report it does, but in my experience it did not and I was unable to figure out why. Beware and be prudent. I will try again if and when Apple announces it officially supports APFS on RAID (which I assume they will do at some ppint, just as they have promised to make it available on hybrid Fusion Drives).

Is there anything any of you could recommend I try before I resort to reverting to HPS+? I am very religious about my backup policy and therefore I have no qualms about running RAID-0 in terms of reliability. The question is whether I can somehow make the existing situation bootable or whether it is a foregoing conclusion.

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    Are you open for alternative solutions? If APFS won’t work for you with RAID, and you’re reluctant to return to HFS+, and are willing to invest a little time to experiment before you get back up running, you may want to check out ZFS on Mac. It is not endorsed or supported by Apple, nor is it exactly made for command-line-averse people. I would only recommend to use ZFS in production if there’s no satisfactory Apple-supported alternative. That said, ZFS is known to work with Sierra, and – as an OpenZFS port – it comes with built-in RAID and unlike APFS, also with block-level data integrity. – Synoli Nov 23 '17 at 8:04
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    I have actually used ZFS on OS X for the sake of experimentation, but it's not really the right choice for this situation. I'm OK with using Apple technologies in unorthodox contexts, but I don't really want to stray that far in a critical production workstation. – James Junghanns Nov 23 '17 at 8:44

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