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).
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.
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.
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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