I recently had an 10.13.4 update problem and while trying to fix it I ended up "corrupting" completely my "Boot OS X" partition files. while my Fusion drive partition was updated correctly to 10.13.4, I couldn't boot from it any more.

Is there documentation anywhere about the "Boot OS X" usage and functionalities. Is there a way to restore it to boot the fusion drive correctly in case of i.e. I deleted all files that are in this "Boot OS X" partition ?

I understood that this partition has the correct kextcache and prelinked kernel of the fusion drive, but is there any other use to the partition.

The following is off subject from my question, but to correct my problem I ended up doing a CCC clone of my "Macintosh HD" fusion drive partition to regular drive. destroy the fusion drive and create a new one. Then did the CCC clone back from the regular drive to the Fusion drive. How could I have avoided that fusion drive fresh creation and cloning job.


If the partition is there, but the files are corrupted, just remove them, boot to a rescue system or installer, open a shell and run touch /Volumes/Macintosh\ HD/System/Library/Extensions or kextcache -i /Volumes/Macintosh\ HD, with Macintosh HD being the name of your Fusion Drive/the mount point. After a while (or during shutdown), the booter should be regenerated.

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