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[Solved] 6540 Big Sur / Opencore: media bay disk not reading properly.


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I have nearly all of my Big Sur installation working in my i7 6540.  Started out with the EFI from the post by takiller in the Big Sur Beta section of the forums. Had a few issues with it at first, but seem to have figured out almost all the little glitches. I have the keyboard and trackpad working even in the installer. I have the Radeon 8790M card disabled, and video working just fine. Sleep works. Got my wireless working with the Azurewave AW-CE123H (BCM4352). Even have filevault working just fine now. And the 11.2 update that just dropped installed without a problem. Only thing I haven't checked at this point is the HDMI output.


But I'm having an issue with the media drive bay not reading properly in one configuration, and I cant figure it out. I have the OS on a drive in the mSata slot. No problems there. I also have a second regular SSD in the normal drive position at the moment (which will soon get replaced by another 2TB HDD). No problems there either. And in the media bay is a regular 2TB drive. The media bay drive is not readable. Says I have to initialise it, but won't format properly for some reason. Errors out with at the last sector. In troubleshooting, I switched out the 2 drives, and the 2TB drive then works just fine in the regular drive bay, and the SSD then works ok, but only shows up occasionally, in the media drive bay for some odd reason. Hopefully that makes sense?


Searching around, some people were suggesting to try adding a couple of different AHCI kexts in the EFI for their Catalina installations with opencore, but I had no luck with that method. Maybe that's a Big Sur issue?  It only seemed to guarantee that the SSD would be seen more consistently, but not the spindle drive. Under Clover, there was a patch that fixed this, but I'm not sure if that's a possible solution? Or where to even put it if it is? Or is there another method to fix this? I've spent the past week trying to somewhat figure out OpenCore, and fix the kinks I had with all the issues so far, but this last one has got me stumped, as there aren't any discussions out there of this with opencore and Big Sur that I could find.


I have linked both IOreg files from when the drives were in both positions. IOreg file numbered 1 is when the spinning drive is in the media bay and not working. And file numbered 2 is when the SSD is in the media bay, and working. Also my current EFI is linked as well. Any guidance would be greatly appreciated.




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Issues with disks in Media Bay have been discussed in the past, mostly for E6x30 if I recollect properly. Did you check these out? Basically, you need to patch AppleAHCIPort kext. You'll find details on the forum in threads such as these:




Can't say if the patch remains the same in Big Sur but look it up.

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Got it fixed.  Had been using Plist Edit Pro to modify my config plist.  Doesn't really give any pointers on how to do the patch like we used to be able to do with Clover Configurator in the past.  Downloaded Opencore Configurator, and was able to figure out where and what fields are needed to input to patch the AHCI.  Wish I had used that to begin with.  Would have made life much easier.  I updated the EFI linked above with the patch for anyone that wants to use it.

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