Windows 10-Upgrade: "Disk Controller: Current Active partition is compressed"

Some users of Windows 7 SP1 (and probably Windows 8.1) are facing a curious error during upgrade attempt to Windows 10. The upgrade wizard refuses an upgrade with a note “Disk Controller: Current Active partition is compressed”. Here a few hints how to proceed.


Recently I stumbled upon this issue in a German Microsoft Answers forum entry. But a short internet search shows, that several cases has been raised up since mid June 2016 (here, here, here). The error will be reported from compatibility wizard during checking Windows 7 SP1 for compatibility before upgrading to Windows 10. The screenshot below has been made in a German Windows 7 (I haven’t an English screenshot).

Upgrade-Assistent Fehler

A typical recommendation (see) is to “check, whether the Windows install partition is compressed or not”. While it looks “nice”, it’s the wrong approach. So I decided to track things a bit down. 

Which partition is active?

Before we try to check the logical drive’s compression flag, it would be wise, to check which partition is active.

1. Enter comp in the Windows 7 start menu search bar and select Computer Management with a right mouse click.


2. Launch Computer Management using context menu entry Run as administrator.

3. Navigate in the left pane to Storage/Disk Management and wait, till the disks are shown (see also here and here).

Side note: The problem should only occur on BIOS/MBR disks, because GTP disks on UEFI systems doesn’t have an active partition. UEFI systems uses an EFI partition to boot. The screen shot shown above has been taken on an UEFI/GPT disk.

Here is another screenshot from a BIOS/MBR disk. The screenshot shown above indicates, that the partition “System Reserved” is the active one. So it doesn’t make sense to recommend “checking the Windows drive for compression flag”. 

Grant a drive number to active partition

If partition Sytem Reserved is set to “Active”, assign a drive letter, using Disk Management.

1. Right click the active partition in Disk Management and select Change Drive Letter and Paths.

2. Assign a drive letter in the dialog box shown using the Add button.

Note: Keep in mind, to remove the drive letter, after you have checked the compression flag as discussed below.

Is the partition compressed?

After assigning a drive letter to the active partition, check the compression flag, using the steps below.

1. Open explorer window, right click the logical drive containing the active partition.

2. Use context menu entry Properties and select the General tab (as shown below in the sample screen shot – but note, the disk isn’t necessary drive C:). 


If the check box Compress this drive to save disk space is checked, the root cause for the error is found. In this case, uncompressing the drive is recommended (see below).  

Some additional theories

If the active disk isn’t compressed, but upgrade wizard reports the error mentioned above, the question is “why”. Here are a few theories.

  • A tool left the active partition in an inconsistent state, so an internal compression flag is set. Try to invoke an administrative command prompt windows and use the command chkdsk x: /x /r (where x: is the active partition drive letter). The command tries to check an repair the drive. 
  • There is a possibility to compress the Master File Table (MFT) of a NTFS partition. This is offered by third party defrag tools and I’ve seen it in Paragon Disk Manager Suite.
  • Maybe an OEM has compressed the partition (first I thought WIMBoot in Windows 8.1 can be a root cause, but we have UEFI systems for WIMBoot). I guess, it’s unlikely the cause, because the error has been observed under Windows 7 (there is no WIMBoot).
  • Also third party tools like VeraCrypt are probably not the root cause.
  • An install on a VHD/VHDX disk can’t be the case, because VHD/VHDX installs are not upgradeable.

Because the error has been observed since mid June 2016, I guess it can be related to some of the compatibility updates (maybe it’s just a bug). But I haven’t had a system with this error to do some further research. If somebody is hit by the error, just try to uninstall June 2016 updates to verify this theory.

How to fix the error

If the hints given above doesn’t deliver a clue, download Windows 10 as an install image using Media Creation Tool and do a Clean Install. My MVP colleague Andre Da Costa has outlined the steps here.

Another trick is to set another partition (the Windows install partition) active. But this can cause other conflicts. Perhaps the hints given above helps to find the root cause. If someone finds an explanation, feel free to left a comment. 

Similar articles
Win 10 Wiki
Windows 10: Open command prompt window as administrator
Trick: How to upgrade to Windows 10 using a clean install
Check and repair Windows system files and component store


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15 Responses to Windows 10-Upgrade: "Disk Controller: Current Active partition is compressed"

  1. M says:

    Last day to upgrade, I left it to last minute, as usual. Had the same compressed error. I just did the right click and set the C to active and did not see the error anymore.

  2. KrzysztofL says:

    Thank you for this post and the tip with Computer Management as a tool for partition management (I didn’t know it). My computer is an msi with OEM Windows and recovery partition which was set active. As soon as I moved activity status from recovery partition to windows partition – problem disappeared.
    I think – this could be common for many notebooks with OEM Windows.

  3. guenni says:

    Thx for confirming the “set Windows partition as active” trick works. But other readers should be warned – the trick works only, if the upgrade is made immediately. Trying to reboot after switching the active partition may result in a non booteable system.

  4. Doug says:

    As with the first comment above, I used the disk management tool, to set my main drive C as active, and the problem went away. Thank you SO much.. NOT my computer is also a MSI, with a recovery partition, that was set to active, and probably is compressed.

  5. bharath r says:

    I had two errors
    1. windows is not genuine , after 2-3 attempts contacting to Microsoft one of the technician helped me in making it genuine.
    2.the above error, in my case active partition was system reserved disk which took me long time to find out.
    luckily i got the free upgrade link to windows 10 from the same technician.

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  7. Gerard D Gilles says:

    here is my problem. I did upgrade from win8 to win10 with any problem of this sort. But, when I tried to update my win10, I received this error message: could not update because the active partition is compressed. What should I do to update?

    • guenni says:

      Try a clean install using Media Creation Tool – or use the advices given above (risky for unexperienced users).

  8. Andy says:

    The 100mb active partition does not allow me to right click and assign a drive letter. When I right click the only menu item is “help”. I cannot make the partition visible, and thus cannot check if it is compressed or not

  9. cat1092 says:

    Andy, by now you’ve found a solution I hope.

    Anyway, MiniTool Partition Wizard is the tool for the job. Install & open that, then click onto (highlight) & assign a letter to the 100MB partition, ‘Z’ is OK. Then click Apply at the top, and this will take place. Now you can uncompress the space.

    Be sure afterwards to undo the letter change, by the same method, click onto & highlight and select ‘none’, then Apply at the top. Now it’s hidden again.

    Easy peasy.


  10. Jose says:

    Thank you. For you help now I can download the update.

  11. Jim Sutton says:

    I have a WIN7 machine which was automatically upgraded to WIN10 my MS.
    Now I have this compressed disk problem. C:drive Properties has a CHECK in the compress this drive disk. But I get a host of host swap file errors when running the uncompression even as PROCESSING streams through indicating 7 to 22 to 1 hours remaining.

    My C:drive is the active partition.

    I got a few email responses from the MS Admins and followed their suggestion while reporting all the results, responses, and failures. Then they quit responding/helping.

    I began deleting the 2016 updates to remove them. Five apparently cannot be removed as the uninstall option isn’t presented. But I can confirm there is no June 2016 dated Windows Updates.

    And Windows Update is now trying to update to version 1709.


  12. Jim says:


    It seems deleting the several Windows Update 2016 entries , that I was able to delete, has done the trick. I ran windows update and it downloaded several updates and restarted multiple times but this morning I have Windows 10 Fall Creators Update running. Success!

    Thanks for this post.

  13. Christine Strachan says:

    I was in the right direction but thanks to me googling and you having this website it looks like I’ve got it covered..
    From processing now on screen it is going to take a while to sort but I feel confident now that it will be fixed and I will be able update and get a better thankyou.

  14. Christine Strachan says:

    I followed the instructions on screen it took over 7 hours but it is now done. Thankyou 😁😁😁

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