I'm having trouble getting my 2015 5k iMac to boot from an external SSD with Windows 10 on it.
Edit:
This thread addressed my issue:
https://forums.macrumors.com/threads/bootcamp-windows-10-from-external-drive.1815672/page-8
It turns out newer Macs have a different way of booting and no longer support the legacy mode, so a lot of instructions for how to install Windows on an external drive will no longer work with newer machines. If your computer is NOT on this list: https://support.apple.com/en-us/HT201518 then you probably have a new machine and need to follow yjchua95's instructions in the linked thread above.
----- original post, for posterity, in case someone comes across this by Googling -----
I installed Windows 10 on an external SSD, and it works fine on my 2012 iMac, but the exact same drive can not be used to boot on a 2015 iMac — it tells me the drive cannot be blessed. I can't get the drive to work on my 2015 MacBook retina for the same reason and errors. The drive simply does not show up when I press option at startup and Boot Champ gives me the "bless failed" "FI found at IODeviceTree:/efi"... error.
diskutil list tells me that my Bootcamp is on a 2-partition drive using the FDisk_partition_scheme and the Type is WINDOWS_NTFS for my BOOTCAMP drive on disk1s2.
Does anyone have external Windows booting working for their 2015 Macs, and have any pointers on what I should do to make it work? It is too bad that the Boot Camp Assistant does not normally support external installs of Windows! All three computers are on 10.11.6 and it does not appear the issue is related to SIP (I have tried both off and on, and it changes nothing for bless).
I suspect the problem is due to the FDisk_partition_scheme on the external rather than the GUID, but if that was such a huge problem, why does it work fine on my 2012 iMac but not the 2015 Macs? I get that things change, but I can't figure out the issue specifically, and if I reinstalled Windows on the external drive it's going to do the same thing again unless I can somehow force it to be on a GUID table (?).
E: I just noticed I had OSXFuse installed on the 2012 iMac but not the others, but installing this and resetting didn't appear to change anything re: FDisk. Reading through a lot of these historical threads and tons of people are saying "you can't install windows to an external drive", ha. Plenty of good info, but oddly can't find anyone with my exact problem. I'm largely following the instructions from https://medium.com/@obezuk/how-to-run-bootcamp-windows-10-on-a-usb3-86551dc3def8#.190gurr49
E2: Ok, now maybe I got it... I reformatted the drive in Disk Utility to use GUID, then I formatted the largest sector of the drive to NTFS, now reinstalling Windows 10 on that to see if it's happy. Fingers crossed.
E3: Nope, that did not work. Now it's GUID_partition_scheme, disk1s1 is EFI (name EFI) and disk1s2 is Microsoft Basic Data, name Untitled. Boots fine into Win 10 on my 2012 iMac, but not on my 2015 MacBook. Will try the 2015 iMac later, but I am guessing it will have the same problem. FDisk_partition_scheme did not appear to matter.
Edit:
This thread addressed my issue:
https://forums.macrumors.com/threads/bootcamp-windows-10-from-external-drive.1815672/page-8
It turns out newer Macs have a different way of booting and no longer support the legacy mode, so a lot of instructions for how to install Windows on an external drive will no longer work with newer machines. If your computer is NOT on this list: https://support.apple.com/en-us/HT201518 then you probably have a new machine and need to follow yjchua95's instructions in the linked thread above.
----- original post, for posterity, in case someone comes across this by Googling -----
I installed Windows 10 on an external SSD, and it works fine on my 2012 iMac, but the exact same drive can not be used to boot on a 2015 iMac — it tells me the drive cannot be blessed. I can't get the drive to work on my 2015 MacBook retina for the same reason and errors. The drive simply does not show up when I press option at startup and Boot Champ gives me the "bless failed" "FI found at IODeviceTree:/efi"... error.
diskutil list tells me that my Bootcamp is on a 2-partition drive using the FDisk_partition_scheme and the Type is WINDOWS_NTFS for my BOOTCAMP drive on disk1s2.
Does anyone have external Windows booting working for their 2015 Macs, and have any pointers on what I should do to make it work? It is too bad that the Boot Camp Assistant does not normally support external installs of Windows! All three computers are on 10.11.6 and it does not appear the issue is related to SIP (I have tried both off and on, and it changes nothing for bless).
I suspect the problem is due to the FDisk_partition_scheme on the external rather than the GUID, but if that was such a huge problem, why does it work fine on my 2012 iMac but not the 2015 Macs? I get that things change, but I can't figure out the issue specifically, and if I reinstalled Windows on the external drive it's going to do the same thing again unless I can somehow force it to be on a GUID table (?).
E: I just noticed I had OSXFuse installed on the 2012 iMac but not the others, but installing this and resetting didn't appear to change anything re: FDisk. Reading through a lot of these historical threads and tons of people are saying "you can't install windows to an external drive", ha. Plenty of good info, but oddly can't find anyone with my exact problem. I'm largely following the instructions from https://medium.com/@obezuk/how-to-run-bootcamp-windows-10-on-a-usb3-86551dc3def8#.190gurr49
E2: Ok, now maybe I got it... I reformatted the drive in Disk Utility to use GUID, then I formatted the largest sector of the drive to NTFS, now reinstalling Windows 10 on that to see if it's happy. Fingers crossed.
E3: Nope, that did not work. Now it's GUID_partition_scheme, disk1s1 is EFI (name EFI) and disk1s2 is Microsoft Basic Data, name Untitled. Boots fine into Win 10 on my 2012 iMac, but not on my 2015 MacBook. Will try the 2015 iMac later, but I am guessing it will have the same problem. FDisk_partition_scheme did not appear to matter.
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