What's The Difference Between CHKDSK /F And CHKDSK /R?

How much do you want to check?

by Leo A. Notenboom

CHKDSK is a powerful Windows utility used to diagnose and repair disks. /F and /R represent two types of repairs.

Chkdsk is a Windows utility that diagnoses and possibly repairs disk issues. It has several options, but the two most commonly cited are /F, for fix, and /R, for repair.

Wait.

Aren’t “fix” and “repair” just two words for the same thing?

Yes. But when it comes to CHKDSK, no.

CHKDSK /F or /R?

CHKDSK /F scans for and attempts to repair errors in the file system overhead information stored on a disk. CHKDSK /R includes /F, but also scans the entire disk surface for physical errors and attempts to repair them as well. Repairs are often successful, but not guaranteed.

Fix: CHKDSK /F

While “fix” and “repair” are synonyms in English, CHKDSK uses them to mean two different things.

CHKDSK /F is concerned with the file system overhead information that tells Windows about the files, folders, and data on the disk and their disk locations.

Think of it as the Table of Contents to a book. CHKDSK /F makes sure the Table of Contents entries all point to the right chapters, that all chapters have entries, and that the page numbers and spelling of the entries are correct.

It’s all about making sure the Table of Contents is correct and leads you to the right information in the book, and that all the information in the book can be found via the Table of Contents.

Back in disk terms, it’s all about making sure that the file system overhead information is correct, leading Windows to the right data on the disk, and that all the data on the disk is correctly represented in the filesystem information.

If errors are found, CHKDSK /F does its best to repair the information, though it’s not always possible.

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Related

If you’ve ever had to run CHKDSK on boot because the drive is in use when you tried to run it normally, you might wonder where the results went. How Do I See the Results of a CHKDSK that Ran on Boot? has the answer.

Repair – CHKDSK /R

CHKDSK /R begins by performing the same function as CHKDSK /F. (This implies that “CHKDSK /F /R” is redundant, as /R includes /F.) CHKDSK /R is also concerned with the physical condition of the information stored on the disk — more specifically, whether or not the data is readable.

Think of this as carefully examining our book page by page to make sure that all the text is legible and no pages are torn. This step doesn’t care what’s on the pages; only that they can be read and aren’t damaged.

In disk terms, CHKDSK /R scans the entire disk surface, sector by sector, to make sure every sector can be read properly. As a result, a CHKDSK /R takes significantly longer than /F, since it’s concerned with the entire surface of the disk, not just the parts involved in the Table of Contents. It carefully examines every single page, not just those referenced by the Table of Contents.

If errors are found, CHKDSK /R does its best to work around them, though it’s not always possible.

If errors are found…

Both /F and /R attempt to fix any errors they find.

CHKDSK /F attempts to build a new Table of Contents, meaning it tries to repair the file system overhead information. Depending on the nature of the errors found, though, CHKDSK may not succeed, resulting in lost files.

Occasionally, CHKDSK /F uncovers information that should be a file, or part of a file, but doesn’t know what to do with it. Then it creates “.CHK” files to contain that information. In our book analogy, it’s like saying “I found these pages, but I have no idea which chapter they belong to.”

CHKDSK /R attempts to use spare disk sectors, if any are available, to take the place of damaged sectors it finds, and then marks the original sector as “bad”, indicating it should no longer be used.

CHKDSK doesn’t cause errors

Because many people first learn about missing files or bad sectors after running CHKDSK, they often blame it for causing those errors. That’s a clear case of shooting the messenger.

CHKDSK doesn’t cause errors; it uncovers them. The errors were already there.

Disk errors happen. Disk failures happen. CHKDSK is one useful tool for recovering from certain types of errors — but you still need to back up. CHKDSK can’t save you from everything, regardless of whether you use /R or /F.

Do this

Run CHKDSK occasionally when you suspect you’re having disk problems. On a disk without issues, it’s completely safe, and if there are issues, repairing them may recover data and/or extend the life of the disk itself.

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Related Questions

Should I use CHKDSK /F or /R?

Whether you use CHKDSK /F or /R depends on the type of problem you suspect and the amount of time you have. If you suspect some data has simply been corrupted, then “/F” is perhaps the better, faster choice. On the other hand, if you suspect a physical issue or damage, then /R will scan the entire surface, though it’ll take longer to do so.

Is CHKDSK /F/R safe?

CHKDSK is safe, but can expose pre-existing problems. Occasionally, files on the problematic disk may be slightly easier to recover prior to running CHKDSK. One approach to protecting yourself is to back up the disk prior to running CHKDSK, if you can.

Can I let CHKDSK /F /R run all night on a conventional HDD?

Yes, it’s not only safe but often recommended that you allow CHKDSK to run until it completes, especially if it appears to be taking a long time. Generally, excessive CHKDSK times indicate a problem with the disk surface, and the extra time is /R doing everything it can to recover data that might otherwise be lost.

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