Partitions missing after installing Windows 10 Anniversary Update

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 everyoneโ€™s input and patience.ย  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 ๐Ÿ™‚ 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?

Posted by on , in Category Windows with Tags
Anand Khanse is the Admin of, a 10-year Microsoft MVP Awardee in Windows (2006-16) & a Windows Insider MVP. Please read the entire post & the comments first, create a System Restore Point before making any changes to your system & be careful about any 3rd-party offers while installing freeware.


  1. Russ Soule

    “trust us” is the ame thing we hear from politicians who NEVER fix the problems they have created. not sure if we should “trust us” when it is Microsoft doing the asking.

  2. Marcus

    I remember having a situation like this after an Windows 8.1 update. I had lost my E partition, it would show as unformatted space. So I formatted it got it back empty of course but got it back. Next thing I know after a restarting I lost it again. After doing some research I found the problem to be in the registry HKEY_LOCAL_MACHINESYSTEMMountedDevices where the lost partition would show as unmounted but I am not sure it was a while back and deleting the unmounted partition entry and restarting the computer would fix the problem.

  3. Janet Chubb

    I have windows 10 on my pc for a couple of months. a large update I tried to put on last night at 7 PM my time. The update was still running this morning just about 12 hours. What is the problem and do I need this up date. I use my pc for work so cannot be with out it.

  4. Yes, it is best to keep Windows updated. Has the download & installation be completed?

  5. Janet Chubb

    No it was taking over 12 hours to down load, I need my pc for work. So do I really need it. Sound like it is an Anniversary windows that comes after windows 10

  6. You need current updates if you wish to install the next set of updates. But you can continue to work while the downloading is going.

  7. Madeleine Alexei

    True, while the Anniversary Update is downloading it is possible to go on using the device. Once it starts applying the update, however, which took about 3 hours on my Core i7-4700MQ laptop, the device is out of action. Fortunately I was out for most of the day and did not need to use it, but some users will not be so fortunate.

  8. Janet Chubb

    I’ll do it on a Sunday, that is the day I do not use the pc that much. This is a pain over 12 to down load? Wish I never got windows 10.

  9. Janet Chubb

    It is the install that is taking over 12 hours. Can you let me know how long the install is? I would say 12 hours is a long time.

  10. My download/install took around 30 mins.

    12 hours is long. ๐Ÿ˜›

    You could do this and try again:

  11. Janet Chubb

    Not mine. ๐Ÿ™

  12. bakabomb

    I have had a lousy experience with my older PC running 32bit Win10 Pro and newer one running 64bit Win10 Home. In the first case the update failed sometime after the “17% complete” while I was out of the room and left me with a blank blue screen, no cursor, no controls including Ctrl-Alt-Del. Had to do a hard shutdown, then on reboot it crashed and I had to restore it to Win10 prior to the update.

    On the newer PC it black screened as soon as it tried to apply the update and I had to revert that one too. You can bet the first thing I did was to turn on the “Delay Updates” option on my Pro machine (and I’m disgusted that the 64bit Home version lacks that option).

    Not happy at all with MS or the half-baked vetting they did on an update that clearly is far from ready for prime time.

  13. Go Kevin

    Partitions missing
    This has worked for me
    A Linux live cd revealed my so called raw partition. It showed me the data, and then allowed me to recover the data to another spare hard drive.
    Doing this if it works you can wait for MS to find the cure,,,,,,,,,,,,, but please do not hold your breath.

  14. Cain Ravenlock

    I suggest you guys use a partitioner like AOMEI partition assistant or any other partition manager that is capable of doing volume conversation. You can use it to try to make your drive active / visible. If it is not recognised at all already from BOOT that means it is the UEFI / efi (bios thing) that cannot recognise the drive.
    This could be because the partition format cannot be read. If your partition is of GPT format then you should convert to MBR NTFS don’t worry a partition manager as I mentioned won’t delete anything on your drive by doing this.
    I had these kind of issues in the past and I hope my newfound knowledge could be of help to you.

  15. bug menot

    “If you try to use 3rd-party software, you could potentially lose all your data.” LULz, there’s your problem. You were running Linux on another partition. ;o Seriously though, did they even say what caused it? Reason not everyone saw this was because most people don’t use multiple partitions on data/external drives, and most don’t dual-boot? Even then, I don’t think everyone in those two situations lost partitions. Makes me wonder just WTH possessed them to touch partition tables for in the first place. This is like the old thing where an unrecognized partition type would still show up as a drive letter, and then it would ask you to format it. I wonder how many accidentally erased their NTFS drives on Windows 98 or Ext4 drives on XP, hehe. BTW, OS/2’s installer used to require you to remove all hard drives besides the system drive, or it would overwrite all their bootloaders. Intuit had a problem where a copy protection vendor overwrote sectors inbetween the MBR and first partition, causing grub to fail, RAID volumes to break, and so on. This was supposed to be an OS-reserved space – oops. So it’s not like Microsoft’s the only one that did this sort of thing.

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