Fsck takes too long on multiply-claimed blocks

Vegard Svanberg vegard at svanberg.no
Thu Feb 12 09:54:40 UTC 2009

After a power failure, a ~500G filesystem crashed. Fsck has been running
for days. The problem seems to be multiply-claimed blocks. Example:

File /directory/file.name/foo (inode #1234567, mod time Tue Feb 
10 08:14:40 2008)
  has 1800000 multiply-claimed block(s), shared with 1 file(s):
(inode #1234567, mod time Wed Dec  1 15:30:00 2008)
Clone multiply-claimed blocks? y 

This takes like forever, probably due to the large number of
multiply-claimed blocks. This number can be from 6-2000000, where the
slow ones are fixed quicky and the large ones takes hours/days.

I was wondering if:

- I can get a list of the impacted files/inodes
- Wipe them with debugfs

Is this safe? How do I do it? Fsck says it's 538 inodes with this
problem. If I could get a file list and be able to wipe the inodes, I
could restore the missing files from backup and get the machine online
again quickly.

Hints/tips? Thanks!

Vegard Svanberg <vegard at svanberg.no> [*Takapa at IRC (EFnet)]

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