Hi,
Microsoft has received a small number of reports of partitions not appearing in File Explorer after installing the Anniversary Update. When viewing the partition in Disk Management, it appears as RAW, unallocated space.
Microsoft is aware of this issue and is working on a solution to be released through Windows Update. Any data you have stored on the affected partition is still there. We recommend that you not try to recover or otherwise write data to the affected partition, nor should you format the partition. We will update this thread when a patch is released. If you would like to be notified when this thread is updated, click the Me Too button at the end of this post.
For up to days 10 days after installing the Anniversary Update, Windows includes the ability to “go back” or return to the previous build if you are experiencing this issue and do not want to wait for the patch to be released.
To uninstall the Anniversary Update:
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Open the Settings app.
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Select Update & security and then the Recovery tab.
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Under “Go back to an earlier build”, click the Get started button and follow the instructions.
(Note: If more than 10 days have elapsed since installing the Anniversary Update or the “Go back” option is otherwise not available; we ask for your patience until a patch can be released. Please check back on this thread for an update.)
Thanks!
Update (9/8/16):
Thanks for everyone’s input and patience. Microsoft is planning to release a fix to address the majority of the misidentified partitions in an upcoming Windows Update.
As part of the Windows Insider Program, users can sign up to receive Windows 10 updates early in order to provide feedback. If you are interested in becoming a Windows Insider, first go to the Windows Insider website and register your Microsoft Account. Then in Windows 10, open Settings, Update and Security and click on Windows Insider Program. You will be asked to associate your Microsoft Account. You can then click the Get Start button. You may be asked to reboot your PC for the change to take effect.
The default setting after joining the Windows Insider Program is to receive early access to updates for Windows 10, Microsoft applications and drivers with minimal risk to your device. It can take a day or more for the change to begin delivering these accelerated updates. As always, you can use the Feedback App to help us improve the product.