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This may seem like an odd question but I was wondering if "chkdsk /r" overwrites all the unused space on a target volume. I understand that the purpose of "chkdsk" is simply to check the disk for errors but I have noticed what happens when you specify the "/r" option considering it has to run through the entire disk surface in this mode and according to Task Manager, it performs some writes during this process. How many? Now that's the question...

The Microsoft docs on the CHKDSK command are pretty sparse on this. Feels like I've Googled everywhere to see if I can gather more details that would indicate so. Wish there was some centralized place to dig deeper on some of the older Win commands. One of those ginormous books you use to hold up your monitor perhaps. 😂

Anyway, I typically use /r with the /scan option and have rather large volumes so it's a little hard to tell what is happening since running "chkdsk /r" takes so long. Most of my hard drives were being read most of the time according to Task Manager and not doing much writing. My main hard drive on the other hand was doing a lot of writing. Task Manager showed it was writing and reading simultaneously nearly the whole time I was watching it. Like I said, my drives are big so I can't just sit there for 18 hours and see what happens. Obviously I don't run with /r all the time or this happens. I did just this once as an experiment.

I only tried /r without the /scan option on one of my larger drives once, but to makes things real simple I finally found a flash drive that was empty and tried it on this. I wanted to test it for NTFS since the /r and /scan options are only available for this format. So I formatted this drive to NTFS and ran "chkdsk /r" on it. I wasn't sure if it would write much, but to my surprise, it looks like it was writing the entire time. It went quick though because it was only 2 gigs.

So now to me, since the documentation doesn't say much on this but from what I can see in Task Manager, "chkdsk /r" does a lot of writing to the disk you run it on. Though I appear to have mixed results and am making guesses from vague documentation and inconclusive observations at this point. Does "chkdsk /r" overwrite all the unused space or only some of it? The reason I'm so curious to know is because having an alternative way to overwrite used space sounds nice. On the Home edition, commands like "cipher" are unavailable and users need to download 3rd party apps to securely wipe free space, typically. If the chkdsk command could do it, that would be kind of handy wouldn't it? Sure, maybe security related things are not its intended usage, but you know what they say: if it works, it's not stupid. 😂😂 After all, there may be many variations and algorithms for a secure free space wipe, but sometimes the best one is a single pass of 1's or 0's if you or someone has a massive drive they've never run it on before.

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  • The help says that it recovers readable information. My understanding has always been that it has to write this recovered information somewhere
    – Rohit Gupta
    Commented Sep 2, 2022 at 23:53
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    I did add clarification. Of course, if errors, some additional space will be used. But not a general overwrite of all unused space and none used if no errors.
    – anon
    Commented Sep 3, 2022 at 0:45

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Does CHKDSK /R overwrite unused space?

No.

CHKDSK looks for errors in the file structure and disk media and if it finds errors, it will attempt to fix if the /f parameter is specified.

If errors are found and corrections attempted, get CHK00001 type of files with the attempted corrections.

Of course error correction will use some space but not a general overwrite of all unused space.

If there are no errors, CHKDSK does not write anything to disk or change the disk structure.

Here is very good Microsoft reading on the topic.

CHKDSK

/r Locates bad sectors and recovers readable information. The disk must be locked. /r includes the functionality of /f, with the additional analysis of physical disk errors.

/f Fixes errors on the disk. The disk must be locked. If chkdsk cannot lock the drive, a message appears that asks you if you want to check the drive the next time you restart the computer

Interrupting chkdsk is not recommended. However, canceling or interrupting chkdsk should not leave the volume any more corrupt than it was before chkdsk was run. <--- this pretty much indicates nothing extra is being written.

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  • I will say, though it was with previous versions of windows, chkdsk, and NTFS, I have had disastrous outcomes canceling chkdsk in progress when it would not stop gracefully. As for reallocating sectors when using /r to check freespace, data recovered from sectors that produce a read error will be written and remapped to sectors set aside on the disk for that purpose. This happens below the filesystem level, however, and is mostly transparent to applications other than chkdsk.
    – Frank Thomas
    Commented Sep 3, 2022 at 0:48
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    I did add the complete article excerpt to remind that stopping CHKDSK is not recommended.
    – anon
    Commented Sep 3, 2022 at 0:52

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