How to dual boot MacOS and UEFI windows 10? too many EFI partition ...

[yashiharu]

I am now really exhausted and overwhelmed after hours of trials and errors, please give me some helpful advice.

I have been using my iMac 2011 for 8 years with dual boot windows 7(BIOS mode) and MacOS.

The optical drive is removed and replaced by an SSD for Windows 7 @SATA port 0 6Gbps
Another SSD for MacOS HS @ SATA port 1 6Gbps
4TB HDD for Data on SATA port 2 3Gbps

Everything works fine.


---- nightmare ----

For the use of eGPU, I have to fresh install windows 10 (UEFI mode) because the eGPU can NEVER be detected in BIO mode and there's no driver for the new AC wifi card with BT4.2 combo card.

I can't remember how everything went south.
First, the 6TB Time Machine HDD dead.

MacOS was accidentally crushed and cannot boot up MacOS, I can only mount it with an external hub to get the data back. And I install a new MacOS HS on a new SSD.

Windows 10 install successfully but after the 1st reboot, it can't boot into windows anymore(black screen 3 beeps, not RAM problem), all recovery methods didn't work.

There're EFI partitions on every single disk.
UEFI Windows 10 required GPT, so EFI partition was created.
MacOS required GPT, so EFI partition was created.
I don't know why there's EFI partition on my 4TB Data HDD and even the new time machine HDD.
I thought EFI partition was the problem, so I tried to delete some of them.

4TB HDD crushed after I deleted the EFI partition ... spent days for the data recovery.

It is really PAINFUL to repeatedly disassemble and put back the iMac components for the NEED of optical drive to install windows. (USB installation method doesn't work on both BIOS or UEFI mode windows installation at all!)

I am now in a mess.
Can anyone give some advice on dual boot OS?

 

[monkeybagel]

diskutil list
/dev/disk0 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *160.0 GB   disk0
   1:                        EFI EFI                     209.7 MB   disk0s1
   2:          Apple_CoreStorage Macintosh HD            159.7 GB   disk0s2
   3:                 Apple_Boot Boot OS X               134.2 MB   disk0s3

/dev/disk1 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk1
   1:                        EFI EFI                     209.7 MB   disk1s1
   2:          Apple_CoreStorage Macintosh HD            999.3 GB   disk1s2
   3:                 Apple_Boot Boot OS X               650.0 MB   disk1s3

/dev/disk2 (internal, virtual):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS Macintosh HD           +1.2 TB     disk2
                                 Logical Volume on disk0s2, disk1s2
                                 E465CEA5-DC55-4E7A-B927-805CEDCE3273
                                 Unencrypted Fusion Drive

/dev/disk4 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *10.0 TB    disk4
   1:                        EFI EFI                     209.7 MB   disk4s1
   2:          Apple_CoreStorage 10TB HFSJ+              10.0 TB    disk4s2
   3:                 Apple_Boot Boot OS X               134.2 MB   disk4s4

/dev/disk5 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                            30_06_2017             *4.7 GB     disk5

/dev/disk6 (external, virtual):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS 10TB HFSJ+             +8.0 TB     disk6
                                 Logical Volume on disk4s2
                                 5899CD10-6612-434C-AFCF-50AF5AF6543B
                                 Unlocked Encrypted

/dev/disk7 (disk image):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        +43.4 MB    disk7
   1:                  Apple_HFS Sublime Text            43.3 MB    disk7s1

/dev/disk8 (disk image):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                            30_06_2017             +311.7 MB   disk8

/dev/disk9 (disk image):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                            1718270100-0001        +512.2 MB   disk9

/dev/disk12 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk12
   1:                        EFI EFI                     209.7 MB   disk12s1
   2:          Apple_CoreStorage Time Machine Backups    999.7 GB   disk12s2
   3:                 Apple_Boot Boot OS X               134.2 MB   disk12s3

/dev/disk13 (external, virtual):

Windows should install in EFI mode from USB2 or USB3 flash drives with no problems. It is normal for an EFI partition to exist on any drives OS X manipulates, so that is not really a bug.