How to unmark an NTFS cluster as bad?

I'll answer the title question nothing more.¹

First, do note that, if the sector is truly bad, unmarking it won't make it readable. So your cloning software is likely to choke on reading it instead.

In NTFS, a cluster is marked as bad by assigning it to a special stream, $BadClus:$Bad, a sparse file.

What you need is to

• edit its runlist to remove the corresponding allocated block(s)
• mark the corresponding cluster(s) as free in $Bitmap.

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• To unmark all bad blocks, there's ntfsfix -b -d (-b=clear bad block list, -d=clear/don't set "dirty" flag) (another method with ntfstruncate does exactly the same²).

  • It might introduce minor inconsistencies into metadata (in my case, a few indices apparently became unsorted), I'm not sure why, so either run chkdsk -f by hand or omit -d to trigger it at Windows startup if / in case you get FS errors.

• To clear a specific block is much more difficult since I didn't find any existing software that can do this out of the box³. NTFS Bad Sectors Resolution: The $BadClus metafile - Katy's code describes the way - basically, it's editing the runlist and bitmap by hand.

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¹ _{Only because handling bad sectors + NTFS + cloning is too broad a topic. I'll gladly answer ones directly related to the matter at hand.}
² _{checked the source code of ntfsfix v2015.3.14.}
³ _{for the insistent ones, these can't do it: ntfscat(can't read unreadable sectors),ntfscp(can't write to offset), ntfstruncate,ntfsfallocate,dd(can't open $BadClus:$Bad for writing)}

I had a hard drive that developed some bad clusters. I replaced it with a known good drive. The restore process restored the bad cluster data as well as the other data. This was on a Windows 7 Enterprise computer.

My solution was to run "chkdsk d: /b" (as has been suggested previously). The /b tells it (for NTFS only) to rescan previously marked bad clusters. At least in my case (and I would suspect all versions that support /b), it clears the bad cluster list immediately before beginning the read scan. Once you see the message "Removing X clusters from the Bad Clusters File" you should be able to kill the chkdsk process (as it is only reading data).

Note: The potential does exist for chkdsk to be updating the bad clusters file at the instant you kill the process if it happened to find a bad sector at the beginning of the drive. I took the risk and it successfully reset the bad clusters file without the need to download a bunch of other programs that require a full chkdsk afterward anyway. YMMV.