XFS, empty files after a crash

[Peter Grandi]

> Hi, After a crash, a lot of files on a xfs file system report
> an empty size with "ls -a" but not with "du". [ ... ]

It is a FAQ:

  http://xfs.org/index.php/XFS_FAQ#Q:_Why_do_I_see_binary_NULLS_in_some_files_after_recovery_when_I_unplugged_the_power.3F

Usually it is a good idea to do a web search before reporting a
problem.

> Is there a way to copy back the used blocks to recover the
> files ?

No, because your applications told XFS that the content of those
blocks could be thrown away in case of crash.

It is your responsibility to ensure that your applications use
'fsync' or at least 'fsyncdata' when data should be stored
permanently before a crash occurs.