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I made an incredibly boneheaded mistake. I typed diskutil cs create Fusion\ Drive disk1 disk2 instead of diskutil cs create Fusion\ Drive disk0 disk1 (while I was looking at the list to make sure I did it correctly—sigh).

That's all I've done. I haven't actually gone ahead with the next step and reformatted the drive with:

 diskutil cs createVolume logicalvolumegroup jhfs+ Macintosh\ HD 100% 

To my understanding, the disks have not been reformatted.

Is it possible to reverse this and get all my data and previous disk formatting back without attempting data recovery (which would require splitting the disks anyway, I believe)?

  • How do I re-fuse an unfused Fusion Drive, ideally without formatting? and looking at man diskutil gives some hints: Perhaps diskutil cs delete lvgUUID followed by diskutil cs revert lvUUID would work? I'm hesitant to try it without confirmation from someone who knows what he's doing because I suspect that I only get one shot at this. – Calion Nov 3 '19 at 15:22
  • Hm…no, that won't work. Under cs delete: "the now-orphaned physical volumes are erased and partition-typed as Journaled HFS+." So close! – Calion Nov 3 '19 at 15:26
  • Oh arg. It may already be too late. Under cs create: "All existing data on the drive(s) will be lost." So the question becomes, How to best attempt data recovery? – Calion Nov 3 '19 at 15:28
  • So I'm guessing that the best way to proceed is to execute diskutil cs deleteVolume on the other disk, then diskutil cs revert on the one I want to save, then use TechTool Pro to try to recover the volume. But advice would certainly be appreciated. – Calion Nov 3 '19 at 21:17
  • The linked question is completely unrelated to your problem! But in most cases at least disk2 may be salvaged. It depends on which of both disks is the faster one... – klanomath Nov 4 '19 at 23:15

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