[German]It worked, the bug I reported about chkdsk ending in an unbootable Windows 10 2004/20H2 on some systems has been fixed. At least that's what the descriptions of update KB4592438 say. Here is a more in depth story about that.
The chkdsk issue in Windows 10
To check a Windows drive for corrupted files, the chkdsk command can be used – where the check is run on the Windows drive by rebooting into Windows PE. But there is a serious issue in the 2004 and 20H2 versions of Windows 10 (and also in current Insider Preview builds). The issue has been triggered after cumulative update KB4592438 was installed.
On some systems, the chkdsk c: /f command caused the Windows drive to become corrupted. The system was subsequently unable to boot after the file check, because the Windows drive was no longer found.
Stopp-Error NTFS File System, Source: planet3dnow.de Forum
The system halts and the blue screen with the stop code NTFS File System shown in the above screenshot occurs. I had covered the problem more extensively here on the blog in the post Windows 10 20H2: ChkDsk damages file system on SSDs with Update KB4592438 installed. It at this time it's still not clear to me, what exactly causes this error, as not all users with the constellation described above get this blue screen. However, after I covered the bug in my blog post, a lot of people read this article. And I've had reported the bug to the developers at Microsoft
Microsoft fixes the issue
Microsoft has now published an addendum in the support article for update KBkb4592438, which describes exactly this bug. There, Microsoft writes that on a smaller number of systems that have this update installed, running chkdsk /f can corrupt the file system and the device may fail to boot.
Microsoft states that this issue is fixed and should be automatically prevented on unmanaged (via WSUS, SCCM, etc.) devices. However, it may take up to 24 hours for the fix to be applied to unmanaged devices. Microsoft states that the fix may be applied to the device faster if users restart Windows 10.
Inside the story
I find it remarkable at this point that Microsoft does not talk about an update rolled out. This means that Microsoft can fiddle remotely with the system. What Microsoft admits is quite intransparent – Albacore addressed his thoughts also within this tweet.
The problem has been introduced with the Servicing_2011c_28083526 feature. Albacore stumbled across my tweet here and posted this tweet about the problem. The bug has been in the system for 8 months, since Windows 10 Insider Build 19624 or 19619.
Instead of using the /f option, it's better to use newer the chkdsk /scan command – which avoids the issue discussed above.
It's not clear to me, how Microsoft is fixing this issue. Within my German blog a reader mentioned, that the group policy
to fix the bug on managed systems contain the following entries:
policies> policy name="KB4586853_Issue_002_Rollback_2020_DEC_19″ class="Machine" displayName="$(string.KB4586853_Issue_002_Rollback_2020_DEC_19)" explainText="$(string.WUKnownIssue_Help)" key="SYSTEM\CurrentControlSet\Policies\Microsoft\FeatureManagement\Overrides"> parentCategory ref="KnownIssueRollback_2004″ /> supportedOn ref="SUPPORTED_Windows_10_0_2004_Only" /> enabledList defaultKey="SYSTEM\CurrentControlSet\Policies\Microsoft\FeatureManagement\Overrides"> item valueName="2372249226″> value> decimal value="1″ /> /value> /item> /enabledList> disabledList defaultKey="SYSTEM\CurrentControlSet\Policies\Microsoft\FeatureManagement\Overrides"> item valueName="2372249226″> value> decimal value="0″ /> /value> /item> /disabledList> /policy> /policies>
It seems that the features management are overrides features provided in Windows 10 20H2 to mitigate the bug. That means, that Windows 10 20H2 probably reads server side which features are available, so chkdsk is able, to detect, which features may be used. Pretty sick 'that whole thing', it would say.
If the system no longer boots
Users who have run into this problem should try booting the system into the Windows PE repair environment – the system should automatically invoke this Windows PE environment after the third unsuccessful boot attempt, if applicable. Then, under Troubleshooting – Advanced Options, go to the command prompt. There, run the command chkdsk /f. The command checks the file system of the Windows drive and repairs the damaged partition structure.
If Windows PE does not boot, you can call up a recovery environment via USB stick or installation ISO DVD and run the chkdsk command from there. However, make sure to select the correct drive where Windows 10 is installed. So removing the corrupted SSD and error checking in a working Windows 10 system is no longer necessary.
For managed devices in enterprise environments, that have this update installed and are experiencing this issue, it can be fixed by installing and configuring a special Group Policy. For more information on the use of Group Policy, Microsoft refers to the Group Policy Overview.
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