Once my external has became too slow I've ran chkdsk /f. And it has found no problems. Next time (in a day approximately) I've ran it it still found no problems in files, indices and security descriptors but went fixing bad blocks in log file after that, then doing something with a bad block file and then with bad block bit map, then hung. I've turned it off, rebooted the computer (and switched the hard drive off and back on (not too quickly)) and ran chkdsk once again. And it hung after verifying security descriptors. Then I've tried chkfdk /r. chkfdk /r has been working more than 20 hours and looks hung now, the output is the following:
C:\Documents and Settings\Administrator>chkdsk f: /r
The type of the file system is NTFS.
Volume label is ntfs-exs.
CHKDSK is verifying files (stage 1 of 5)...
File verification completed.
CHKDSK is verifying indexes (stage 2 of 5)...
Index verification completed.
CHKDSK is verifying security descriptors (stage 3 of 5)...
Security descriptor verification completed.
CHKDSK is verifying file data (stage 4 of 5)...
File data verification completed.
CHKDSK is verifying free space (stage 5 of 5)...
Free space verification is complete.
Onece I've tried to mount the drive in Linux, it says that MFT copies don't match and recommends to run chkdsk in Windows.
Best Answer
It came out (I've used an RS-232 maintenance terminal connection bypassing SATA to diagnose the HDD) that the hard drive had gotten severely damaged and was failing in an avalanche.
I conclude (as I had never (throughout my 12 years experience) seen CHKDISK coming unresponsive) that CHKDISK hanging can probably mean the same (low-level HDD failure) in the most cases and the wisest things to do would be to stop using CHKDSK and either grab all the data readable as quickly as possible or turn the HDD off to prevent further damage and make further data recovery easier.