Huh?

One of the issues experienced by users after installing the Windows 10 Anniversary Update concerns partitions, as many of those who upgraded their computers reported that a number of partitions disappeared from File Explorer.

Furthermore, all partitions show up as RAW in Disk Management, which makes most people believe that all their data has been removed and nothing can be recovered.

Microsoft, however, claims that this is just a bug discovered in the Windows 10 Anniversary Update install system, and while no files are lost, it’s critical for users not to try to recover anything with third-party apps because this could lead to completely breaking down the partitions and removal of data.

Windows 10 Anniversary Update Might Hide Partitions After Install

A few users affected in this thread:
Windows 10 Anniversary update problems, not recognizing external hdd

There was also at least one mention of this happening in the mammoth 'Anniversary Update' thread in the news section.

The key bit is

while no files are lost, it’s critical for users not to try to recover anything with third-party apps because this could lead to completely breaking down the partitions and removal of data.

still happen to me in update 14393.67, it's not Just Bug,it threat to user who dont know, how to recover/not computer geek.

Happened to me on my desktop PC. After the upgrade on first boot to 1607 I got a "missing D:Desktop" error message. Something like that, may not be the exact wording. My secondary data drive was MIA in explorer. Disk management showed it as RAW. I had almost all of it backed up to an external drive. I just repartitioned and reformatted it, and copied my files back. It was a 1TB spinner drive about 3/4 full. My laptop with two SSD's was fine though.

Happened to me on my desktop PC. After the upgrade on first boot to 1607 I got a "missing D:Desktop" error message. Something like that, may not be the exact wording. My secondary data drive was MIA in explorer. Disk management showed it as RAW. I had almost all of it backed up to an external drive. I just repartitioned and reformatted it, and copied my files back. It was a 1TB spinner drive about 3/4 full. My laptop with two SSD's was fine though.

exactly same, 1tB hdd, i delete and recreate that partition, restore file from external media, still happening.

i even reinstall and using windows 8.1 right now.. my pc feel rock solid,stable .
(even i had windows 10 pro 1151 with defer upgrade image.)

Only happened to me the one time on the one PC during the upgrade. I did a clean install after that and all was fine. That drive stayed visible.

The key bit is

while no files are lost, it’s critical for users not to try to recover anything with third-party apps because this could lead to completely breaking down the partitions and removal of data.

Huh?

Users can't access their data and MS says don't try to recover it?
What are they supposed to do?

I suppose MS' next suggestion will be to store all of your files on OneDrive.

Sounds like I'm lucky that my Activated versions of W10 won't locate the Anniversary Update.

Got my 14901 build installed through USB. The traditional WU method failed to work on my laptop and on my desktop, the build was never detected. Both times I installed through USB and worked flawlessly. Weird.

Also discovered a bug: when you click on the personalization option in the Settings app, the app immediately crashes. Anyone else getting this problem?

Well this is yet another fine example of poor software QA from Microsoft. I've deferred upgrades until this and other problems are fixed.

2 physical machines +1 VM=no problems
I wonder if it is a driver signing thing(chipset, disk controller or Intel Rapid Storage Technology(IRST)), now that it is strictly enforced with Redstone 1.