Over the years, there has been quite a deal of discussion over which order the two system repair commands, sfc /scannow and DISM /Online /Cleanup-Image /RestoreHealth, should be run when trying to resolve issues. First, you’ll need to understand what each command does.
Both commands check for missing system files and system file corruptions, of course, but there is a big difference in the how:
- System File Checker (sfc /scannow): scans for and replaces any corrupt or missing system files with a copy stored locally in the WinSxS folder
- DISM /Online /Cleanup-Image /RestoreHealth replaces any corrupt or missing system files in the local WinSxS folder with those from an online image
From that, it should be pretty obvious that the correct order in which to run the two commands is DISM /Online /Cleanup-Image /RestoreHealth first and sfc /scannow second.
The logic: Considering the SFC command is checking system files against those stored locally, it is essential to first make sure there are no missing or corrupt files in the local WinSxS folder. Once that has been confirmed by running the DISM command, you can then go ahead and run the SFC command, safe in the knowledge that it is checking system files against a known good source.
SFC Scan Results Explained
There are three main results following a completed SFC scan:
- Windows Resource Protection did not find any integrity violations: this is the optimum result, meaning all is well
- Windows Resource Protection found corrupt files and successfully repaired them: this is the next best result, but following this result, you should restart the computer and run the command again
- Windows Resource Protection found corrupt files but was unable to fix some of them: this is not the message you want to see. However, running the DISM command beforehand will help decrease the chances of receiving this message
SFC /Scannow Tip!
Most users only run the sfc /scannow command when they are experiencing issues, which is a mistake. I am not sure how system files go missing or become corrupt, but I know they surely do, and in this case, time is the enemy.
The longer you leave between scans, the more chance there is of missing or corrupt system files, and if those missing or corrupt files accumulate, that’s when you’re more likely to see that dreaded number 3 message.
I run the sfc /scannow command every two weeks, just before I create a new image backup. I am not suggesting you do the same, but I would suggest running the command at least every couple of months, preferably every month.
Rule of thumb: System file corruptions are not necessarily obvious, and the more they accumulate, the less chance there is of a successful repair.
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