Issue With Starting Windows 10 Under Bootcamp On A New IMac Pro

Thank you for responding.

I have done both an SMC reset and I have reset the NVRAM. Neither resolved the issue. I have found that since writing my original post that Windows 10 will not boot with any USB HD plugged in. My two external Thunderbolt HD's cause no problems. I just get the Windows logo and the spinning disk. If I unplug all USB3 external HD's, Windows 10 will boot and after it boots I can plug in the HD's and they are recognized and all is well. I cannot for the life of me figure out why Windows 10 will not boot on this iMac Pro with any USB3 HD's plugged in.

Tom

I am connecting the Western Digital external hard drives to the USB3 ports on the rear of the iMac Pro. No adapters and no USB3 hub is being used. The only other connection to the iMac Pro’s USB3 ports is the keyboard’s Lighting to USB connector.

i have a Pegasus3 R6 raid array attached to one of the four USB-C/Thunderbolt 3 ports and a Western Digital Thunderbolt2 Duo attached to a second USB-C/Thunderbolt 3 port via an Apple Thunderbolt 2 to Thunderbolt 3 adapter.

All Bootcamp drivers were installed during the Bootcamp Assistant installation of Windows 10. In Windows 10 I checked to see that Windows was using the best drivers for the two external USB3 hard drives. Windows reported that it was already using the best driver for each HD. I used WD software to ensure that both external HDs have the latest firmware. They do.

Tom

I have used both externally powered WD USB3 hard drives and a bus-powered USB3 WD hard drive purchased yesterday. In all cases the external USB3 hard drives are ejected 75% of the time (or more) on waking the iMac Pro from sleep.

When in Windows 10 I use the bottcamp tool in the lower right and select boot in MacOS. That has always worked correctly. I know that holding the option key on boot and selecting Windows from the Startup Manager screen does not work when external USB hard drive are connected. I know that when I use System Preferences >Startup Disk and select Bootcamo Disc that Windows 10 will not start UNLESS all external USB3 hard drives are disconnected. If they are disconnected, Windows 10 starts and runs normally.

Tom

I don't attempt to hibernate Windows. The two external USB3 hard drives are ejected and do not appear on the desktop about 75-80% of the time that I wake the iMac Pro from sleep under MacOS High Sierra.

Iam on the latest version of MacOS High Sierra. Going to System Preferences>Startup Disk and selecting the Bootcamp Disk followed by a restart always works unless I have any USB external hard drives plugged into the back of the iMac Pro. If external USB HD's are present, then Windows will hang at the Windows logo screen and the spinning white circle of dots. Removing the external HD's and rebooting, and Windows will always boot.

I have not tried the Option key route lately because a few days ago I thought that it was causing the Windows hang at boot. Now I realize that the Option key has nothing to do with Windows hanging, but rather whether I have USB HD's connected for not. I'll try the Option key boot into Windows, but I suspect it works no differently than the Startup Disk method, and will work only if no USB HD's are connected.

A full diagnostic hardware report on my iMac Pro has been sent to Apple engineers and I am working with a Senior Apple Advisor on the issue.

Tom

I don't know what "HS" is. I have no idea if Windows Fast Start is enabled or not. Where do I find Windows Fast Start?

Tonight I repeatedly tried to boot the iMac Pro into Windows 10 using the Option key on boot up and then selecting Windows in the Startup Manager that appears. Every time I used this method (whether I had external USB drives connected or not) Windows never got past the startup screen. When I used the same method to start up my iMac Pro in MacOS High Sierra, I had no problems doing so. When I used the method of System Preferences > Startup Disk and selected Bootcamp and restarted with no external drives attached, I was able to boot into Windows. When I used this same method with external hard drives attached to the iMac Pro, I could not get past the Windows start up screen. Plugging the HD's into the iMac Pro after Windows was started caused no problems and the HD's were recognized and could be used in Windows.

This iMac Pro has 2TB of flash storage and is APFS formatted. The Bootcamp partition is NTFS formatted. All formatting was done in Apple's Bootcamp Assistant, and no problems were experienced during the partitioning of the Macintosh HD, formation of the Bootcamp partition or installation of Windows 10.

As I have stated previously both of the external HD's are Western Digital. One is a 3 three month old USB3 HD with a power adapter. The other is a new WD My Passport USB3 HD that is bus-powered.

Yes, I can use Windows Bootcamp Control to switch back into MacOS. I have removed both Western Digital USB3 disks, replaced them with a Sandisk 64GB USB3 Extreme flash drive, and I can boot into Windows via System Preferences>Startup Disk and selecting Bootcamp. I cannot boot into Windows 10 with the Sandisk flash drive installed using the Option>Startup Manager>Windows route. I have now removed the Sandisk Extreme USB3 flash drive and installed a USB3 hard drive that is in an Orico External Hard Disk Enclosure which I had been using without problems on my 2008 Mac Pro. I formatted the HD in the Orico Enclosure in HFS+. I can boot into Windows with the Orico USB3 hard drive installed on the iMac Pro using the System Preferences>Startup Disk>Bootcamp method, but not using the Option key on startup. When I wake the iMac Pro with the Orico External HD Enclosure attached, it ejects the USB3 HD and I have to reboot it to get the HD mounted. In other words, the behavior of the Orico External UB3 HD enclosure upon waking my iMac Pro from sleep is the same as with my two WD external HD's.