Some users have reported that after upgrading their computers to Windows 10 Anniversary Update v1607, they have found that one or more of their disk partitions have gone missing, have disappeared or are lost, and the disk space appears as raw unallocated space in Disk Management.
Partitions lost or missing after upgrading Windows 10 to v1607
If you have just installed the update, you may within 10 days rollback your Windows 10 to the earlier version via Settings > Update & Settings > Recovery > Get back to an earlier build. If you have crossed the 10 day period, then you may have a situation on hand!
Microsoft has said that it is aware of the situation and asks for your patience as it plans to release a patch to fix this issue very soon. Till then, it recommends that you do not try to recover that data, nor write data to the affected partition/s, nor should you format the partition.
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, said a Microsoft Forum Moderator on 8th Sept.
Microsoft released a Cumulative Update for Windows 10 v1607, KB3189866 on 13th September. We hope that you have installed this update, as it has fixed the issue for many. But there are yet others for whom this vexed issue remains!
On 14t Sept, a Microsoft employee said on Reddit:
As some of you have gleefully posted, the issue is fixed for you. And I am very glad that you are happy now :) I do understand that there are another set of folks who have applied KB3189866, but still cannot access their drives. We are still working on those variations. So please wait for those fixes to hit Windows Update. Trust us, we are actively working on that.
If KB3189866 has fixed your issue, great! But if you are still facing this problem, we suggest that you wait till Microsoft finds some solution. The data is there, but the OS is not able to find it and is unable to mount the partition. If you try to use 3rd-party software, you could potentially lose all your data.
What has your experience been with the Anniversary Update been so far?