I have various VHDx files on USB connected external SSD drives for recovery etc. and don't have any problems booting and using the systems normally. The only time I run into a problem is when the system enters sleep mode and then shortly after, wakes up with a BSOD "VHD boot initialization failed". I don't have this sleep problem when the active VHDx is located on an internal SSD. I haven't yet figured out the difference between a VHD going to sleep working on an internal drive vs not working on an external drive. I don't want to disable sleep unless there's no way to fix this. Anyone having this problem too or know if this is fixable?
This issue may be related to how Windows handles external USB drives during sleep and wake cycles. When a system enters sleep mode, power to USB ports might be reduced or cut off entirely, which can lead to the external SSD becoming temporarily unavailable. Upon waking up, Windows tries to access the VHDx file, but if the external drive hasn't fully reinitialized yet, it can cause the "VHD boot initialization failed" error. Does your mainboard have have options of usb fast charging in the uefi? I believe usb would still provide power even while windows is asleep. You could also try changing the Advanced Power Settings. Find USB settings > USB selective suspend setting and set it to Disabled. What if you went from Sleep to Hibernate?
Nothing disabled in Advanced Power settings has an effect on the issue. I have a setting in the BIOS called USB always on that I disable. It resolves the issue when enabled, but that means all ports will always be powered on. I don't need that for my attached USB data HD and I want that to spin down normally. I only need the port where I occasionally boot an external SSD drive from to always have power, which my BIOS won't do. It's all or nothing. Disabling Allow the computer to turn off this device to save power in Device Manager also has no effect. I guess I have no choice other than disabling sleep with powercfg for my external bootable VHDs, but that won't resolve the problem with other sleep methods available, so I need to keep this in mind. I think some newer HW have an always on feature for a single USB port.