What does chkdsk do, exactly?

I have attempted to read a bit about chkdsk but I still don't conceptually understand what it does.

From Microsoft: "Creates and displays a status report for a disk based on the file system. Chkdsk also lists and corrects errors on the disk. Used without parameters, chkdsk displays the status of the disk in the current drive."

From Wikipedia: "Displays the file system integrity status of hard disks and floppy disk and can fix logical file system errors."

But this is all extremely vague, and I've not seen a good, concise, clear summary of what is actually going on.

I just ran a chkdsk and got some of the following messages:

Deleting corrupt attribute record (128, "") from file record segment 120759.

The USA check value, 0x0, at block 0x3 is incorrect. The expected value is 0x63.

The multi-sector header signature in file 0x3d5b6 is incorrect.

Deleting corrupt file record segment 251333.

Deleting orphan file record segment 251321.

Deleting an index entry from index $O of file 25.

Deleting index entry P1040158123.JPG in index $I30 of file 118566.

Is there anywhere I can go to make any sense out of any of these messages? Does it matter at all to an end user? Does it ever delete files or only indices? From the log / output it seems like I had a lot of errors in my disk, but don't know if this is something I should be concerned with or not.

Cory

Posted 2010-01-28T15:37:29.693

Reputation: 483

Answers

I think that the Microsoft definition is quite good, from your question-

"Creates and displays a status report for a disk based on the file system. Chkdsk also lists and corrects errors on the disk. Used without parameters, chkdsk displays the status of the disk in the current drive."

From what you have shown, your hard drive basically had a bit of corruption, but it looks like chkdsk was able to fix it.

This sort of thing unfortunately happens over time (bad shutdowns / power failures during writes etc.) and it isn't necessarily anything to be concerned about.

William Hilsum

Posted 2010-01-28T15:37:29.693

Reputation: 111 572

Does this mean that chkdsk never deletes files? That was a major question I had. – Cory – 2010-01-28T16:45:36.150

5chkdsk don't delete files, however it could (partially) recover an already corrupted file to a .chk file. And in case of a serious hard drive failure, the reading/writing can worsen the situation, so the first thing to do is to save important files... – fluxtendu – 2010-01-28T17:17:44.517

1Thanks. I'm still not fully satisfied by this explanation, though. "corrects errors" is so vague. Maybe I should just RTFM. – Cory – 2010-01-28T21:09:50.100

1@Cory: to really know what errors it can correct this would need a thorough explanation of all NTFS features, data structures and inner workings which certainly is possible but not in a meaningful, short way. Basically, everything the file system takes for granted can go awry, and yes, even with a journal (although that enables pretty good self-healing capabilities); if anything is wrong, then you can try fixing it. Read up a bit on how a file system works and then you can probably think of enough cases where something can go wrong and needs fixing. – Joey – 2010-05-02T01:17:38.957

It doesn't delete files per se, but it can do more harm than good if there is deleted/lost data on a drive that you intend to recover, as it can overwrite clusters it considers free. I once destroyed deleted files on a FAT drive by running CHKDSK over it, which made unrecoverable some files that before the scan, an undelete software still reported it could restore. Basically, don't run it on a drive you're already having issues with. – Daniel Saner – 2016-01-09T20:04:24.433

Does chkdsk refresh hard drive data? i.e read every bit and write it back to make sure that magnetic fields stay strong. – Jean – 2017-11-08T20:59:05.553

My 2 cents, mostly for future readers, considering the age of this thread.

Some users are undoubtedly unaware there are really two levels of chkdsk operation, selectable via command line switch: the slash F (chkdsk /f) and the slash R (chkdsk /r). Both instruct chkdsk to fix the errors it finds, but the difference is that slash F does NOT check the drive for bad sectors, whereas slash R does.

One way to think of it is: /F fixes software problems, /R software AND hardware, since bad sectors are actual physical damage to the disk surface. /R does essentially what the old SpinRite program used to do ("used to" because today's large capacity drives are for the most part beyond its abilities to deal with); analyzing every single sector on the drive, whether it contains data or is completely blank, and attempting to read AND relocate data it finds onto good sectors. Then it marks the bad sectors AS bad, so that Windows does NOT use them again, effectively "removing" the bad sectors from the system.

As might be expected, the /R option takes several hours to complete, so don't sit there staring at it waiting for it to finish. :)

I'm generally a huge critic of Microsoft, yet even I have to admit they got it right with this tool; used right it's easily worth the same as standalone programs that sell for anywhere from 40 to 100 dollars (on a separate note: the same can be said about 'defrag' which is also included with Windows; does as good and possibly a better job than commercial defraggers.)

Mike Mounier

Posted 2010-01-28T15:37:29.693

Reputation: 327

Agree with Wil's answer in terms of what the big picture is. You probably don't need to worry what the error messages mean.

That said, if you what the error messages mean, you would need to understand how NTFS/FAT/filesystem of your choosing formats a disk. I think the Russinovich books from Microsoft Press discuss NTFS, and I'm sure there are other free web resources, eg this site seems like a decent NTFS discussion at first glance. But most likely this is more detail than you need to worry about.

dsolimano

Posted 2010-01-28T15:37:29.693

Reputation: 2 778