I have a Mac mini late 2012/2.5 GHz Intel Core i5, with 2 disks, one SSD, and a HDD. The SSD has the most recent High Sierra and the second drive OS X 10.9.5.

After many attempts to force High Sierra to connect my Bluetooth keyboard, I decided to set Maverick as the boot drive and restart to check whether the keyboard is detected there.

In fact, it was, but now it does not mount the SSD with High Sierra and even in the terminal mode I get the message "unknown special file or file system."

Any ideas how to force it to mount again, besides upgrading the 10.9 to Sierra?


Your SSD is formatted to an APFS container with several APFS volumes including the High Sierra system volume.

Mavericks and all other OSs (except Sierra with "experimental support" and High Sierra) natively don't contain drivers to read from or write to APFS. Paragon offers a read-only driver for 10.10-10.12.

Consequently you can't mount APFS in Mavericks.

You can backup your High Sierra volume, reformat the SSD to HFSJ+ or CoreStorage and restore HS there though, but this is not recommended.

So if you want to access files and folders on the High Sierra volume in Mavericks use a third volume (formatted to HFSJ+/CS) as a transitional volume (i.e. copy all required files from HS to this volume to access them from Mavericks).

  • @klanomath but this solution gives me access to the files, but will not allow me to restore to my previous condition as it having High Sierra bootable machine right? So far it seems that I have 2 incompatible conditions, see again the Sierra and the current Maverick and I'll have to upgrade de Maverick disk until it "sees" and mounts the SSD? – jcarlos Mar 2 '18 at 13:02
  • @jcarlos The real problem is your keyboard, isn't it? Is it a original Apple keyboard? – klanomath Mar 2 '18 at 13:05
  • @klanomath it "was" my first problem, this one that prevents me to work on my current OS is now a 10x impacting issue than the keyboard. I just restarted and boot with this old Maverick because I wanted to see if the issue was with the keyboard. I think it will cost me less just to upgrade the Maverick until some new version mounts the SSD. – jcarlos Mar 2 '18 at 13:09

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