A message from Gabriel Aul, on behalf of the Windows 10 team:
Hi everyone,
We recently released an update for the Windows 10 Technical Preview (Build 9879) to fix an issue with frequent Explorer.exe crashes - KB3020114. We’re releasing a few fixes to the most painful issues hitting Windows Insiders on this build since we won’t have a full new build until early 2015, and we want to keep it usable for you through the end of the year.
Unfortunately, as many of you discovered there was a problem that affected about 12% of PCs when installing this update, causing the install to fail.
The issue occurs due to 2 underlying bugs:
In build 9879 we introduced some new System Compression code that systems with SSDs can take advantage of to reduce disk usage by the OS. In some cases the logic for low-space detection gets inverted, and we compress automatically as a background operation.
On PCs have had system compression enabled, an additional bug with how the filesystem tracks deletes caused the installer to think that the temp files failed to extract correctly, so the installer fails because it thinks it cannot complete.
Workaround
For the short term, anyone affected by this can get past it with the following workaround:
Restart your PC
Open CMD.exe as an Administrator and run: compact /u /exe /s:%windir%\winsxs\filemaps
Immediately afterwards run Windows Update and Check for Updates
Install KB 3020114
Restart when prompted
What’s next
On a shipping OS, if we hit an issue like this we’d normally pull the update. But since the Windows Insider audience is technical we decided to leave it up while we work on the fix so that people hitting the Explorer crash can get some relief. We need to fix the 2 underlying issues above, and make sure that no additional problems prevent hotfix installs in the process. We’ve been working on this since last week but it will take a bit more time to ensure we got it right.
We appreciate your patience on this, and again THANK YOU for being a Windows Insider. While bumps like this are unfortunate they are a part of engineering a new OS. You’re seeing everything early (flaws and all) as we build this together. The good news is that your help is allowing us to find and fix these issues much faster than in the past, which means that the final product will be higher quality as well as having features shaped by your feedback.
Thanks,
g