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UEFI/MBR/Partition Issues after Windows 10 Update

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Sorry for the unclear title, but I'm struggling to properly define this :)

I've been dual-booting Sierra and Windows 10 on separate SSDs for months without issue. I'm using UEFI and my Mac drive has always been the default.

Yesterday, I booted over to Windows 10 to do some stuff and I let it get caught up on updates/patches. I shutdown and restarted, and the system booted into Windows 10 right away. I shutdown again, and went into the BIOS and didn't see any of my Mac SSD UEFI partitions as an option for booting.

Since then, I've done some messing around with fdisk (from Recovery) and setting various partitions to active, but I'm still unable to get my Mac SSD UEFI partitions to show up in the BIOS as a boot option. I created a Clover USB drive on another Mac, so I can now finally get into my SSD and boot into OS X, but of course, my sound drivers aren't loading. There have been a couple of times where I do see the SSD's UEFI partitions as boot options, but they always disappear on the next boot.

Is it possible that the Windows 10 updates messed with the MBR on my Mac SSD or is this unrelated and is my SSD failing? Once I'm in the OS, everything is fine (except for sound), and I haven't had any other issues on this build. Is there any reason why the BIOS would be inconsistent with what it sees as boot options?


Here's how gdisk sees my current partition table on the Mac SSD

Code:
Warning: Devices opened with shared lock will not have their
partition table automatically reloaded!
Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.

Code:
Disk /dev/disk1: 1465149168 sectors, 698.6 GiB
Sector size (logical): 512 bytes
Disk identifier (GUID): 59A3C714-1555-44CE-A40A-2E5005607770
Partition table holds up to 128 entries
Main partition table begins at sector 2 and ends at sector 33
First usable sector is 34, last usable sector is 1465149134
Partitions will be aligned on 8-sector boundaries
Total free space is 13 sectors (6.5 KiB)

Number  Start (sector)    End (sector)  Size       Code  Name
   1              40          409639   200.0 MiB   EF00  EFI System Partition
   2          409640      1463879591   697.8 GiB   AF00
   3      1463879592      1465149127   619.9 MiB   AB00

Now that I can at least boot up using USB, I don't want to mess with fdisk/gdisk anymore without checking here to see if there's something obvious I'm missing.

Thanks for any help!
 
Last edited:
Disconnect Win10 drive, boot to UEFI and set the Mac OS drive as first in BBS boot order, save&exit, continue boot.
Reboot, shutdown and boot several times to make sure the Mac drive is operating properly.
Then shut down, connect the Win10 drive, boot to UEFI and again set the Mac drive as first in BBS boot order.
 
Disconnect Win10 drive, boot to UEFI and set the Mac OS drive as first in BBS boot order, save&exit, continue boot.
Reboot, shutdown and boot several times to make sure the Mac drive is operating properly.
Then shut down, connect the Win10 drive, boot to UEFI and again set the Mac drive as first in BBS boot order.

Thanks for the reply!

The BIOS doesn't see the UEFI partition of my Mac SSD even with the other drives disconnected.

It does see the physical drive "P0: Crucial_CT750MC300SSD1" but when I try to boot from that, I get the boot0 error (attached)
 

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Sure enough, some magic with gdisk and I'm back and running - I haven't booted back in and out of Windows 10 yet (fear), but I can now boot Clover directly from my SSD and the UEFI option shows in my BIOS.

While I was troubleshooting initially, I was looking at some guides for fdisk and I did an "fdisk -u" to my SSD, which seems to have messed up the MBR. I found some other guides, and creating a new protective MBR with gdisk fixed it.

Thanks again!
 
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