Q: Windows 10 upgrade fail 80073B92-20009 Fusion Drive iMac

Same exact issue, same error.

Still haven't gotten it to work...

Windows 8.1 via bootcamp, running great otherwise... but Windows 10 upgrade fails at "copying files" with that same error code.

Windows hilariously downloads the entire 2.6 GBs again on each attempt (sigh), but frustrating.

I'm having the same problem on my 5K iMac.

Out of curiosity, where did you get your copy of 8.1. Mine was a discounted version through work. I noticed a thread here  where someone said that MSDN versions of 8.1 can't be upgraded using windows update and need to be updated using a separate installer. Worried that I'm having the same problem here.

The thread also suggests that second hard drives have been known to cause problems so have unplugged mine. Now waiting for the 2.7GB download to complete again.

It is not Windows fault you wasted hours trying to install an unsupported operating system using Boot Camp. Wait until Apple releases the Windows 10 Boot Camp drivers then try again.

Unplugging the external hard drive didn't help

It is not a Bootcamp driver problem, other people have no problem upgrading to Windows 10...

Not a bootcamp problem, but likely a fusion drive problem.

Many people on Windows machines reported this error when they have multiple drives.  Unplugging the other drive allowed installation.  The Fusion Drive is a regular drive and SSD combination, but we can't unplug one of them to continue installation.

So it's an issue between win10 and the imac fusion drive, which is why not everyone on a mac has this problem, but those with fusion drives do.

I wonder if there is any fix that is really possible. I'd like to upgrafe and then do a clean install, but I can't do that without upgrading first.

Good news. Bootcamp Software was just updated to 6.0 with Windows 10 support. Yay!

https://twitter.com/MacRumors/status/631685812984266752

To download just use your already installed Bootcamp Assistant, tell it to download the latest support software and it'll download the latest (it took a bit of time).

I don't think this will help.

This is a Microsoft/Windows problem.

You're right, I totally posted that on the wrong thread, my apologies. As for your problem, I'd make sure you have no USB drives plugged in. Sounds kinda like an issue I had when I updated and that's what fixed it, unplugging the other drives. Your mileage may vary. Good luck.

So glad I found this thread, the past couple days have been miserable. I have the same exact issue, same error code and same blink of the installation circle before rebooting back into 8.1. Several hours spent trying solution after solution from all over the internet and I have tried everything, from checking disk for errors and fixing it to system defragment, same error every single time. Every attempt to update also brings up the 2GB download which just gets on my nerves and I'm a gamer so I have pretty fast wifi, my 2GB finished in like 5-8 minutes and that itself annoys me so I can imagine other people who spend hours waiting.

Seeing that the bootcamp 6 was out i was finially excited thinking it would fix the issue, trying to install bootcamp 6 itself was such a pain, I had to download the previous version of bootcamp, run it and repair it before running bootcamp 6 off of a flash drive; for some reason the apple software update just wouldnt show bootcamp 6 as an update. So anyways, after bring it up to date i was excited, thought this was finally it and like britops mentioned above, everything happened in the same order with the same error fail code.

My only differences is, 1 i'm not sure if mine is a fusion drive, im using the 250gb macbook pro late 2013 and i actually have my windows partition installed on a separate western digital 1TB hardrive (no way was I gonna split the 250gb or mac and windows, i wouldnt have enough space to even install 1 game).

From all the reading and reasearch i have done on this error code, it seems to me that perhaps this error only pops up on people who run 2 different OS. I was reading on another forum about some people running linux and windows and they mentioned about disabling the linux partition which fixed this exact error and after updating to windows 10 they reconfigured the linux partition. Some people were also suggesting to unplug the drive from the computer which I think could solve the problem but i dont think that is possible on any macs in the recent years. I suspect this issue is on hands to fix, not apple as people dual booting with linux also expirence the exact error.

Would be so gad if someone manages to find a fix or work around that doesnt involve doing a fresh install of windows.