Re: reiserfs3, rsync and hardlinks

[Chris Mason <mason@suse.com>]

On Monday 07 February 2005 15:50, Pierre Etchemaite wrote:
> Le lun 07 fév 2005 13:22:51 CET, Vladimir Saveliev <vs@namesys.com> a écrit
>
> > Hello
>
> 	Hi,
>
> > yes, reiserfs reuses inode number of removed files for newly created
> > files. However, ext2 also does that. Have  you ever noticed this problem
> > on other filesystems?
>
> No, but I'm only using rsync -H for a few weeks. The problem may also exist
> with tar, but unnoticed (unless tar detects hardlinks in a different way,
> or does more checks, like checking the consistency with references
> counters, whatever, to avoid it). rsync handles hardlinks in a final pass,
> so as soon as the verbosity level is raised, problems are easy to detect.
>
> I have only one server left that uses ext2. It's also saved with rsync, no
> problem seen so far (a few weeks only, as I said).
> But the filesystem used isn't the only difference. Usage pattern probably
> matters a lot. On the system where it happens, hardlinked files are often
> Maildir files (unsurprizingly) and mrtg log files (which are rotated every
> 5 minutes). inodes are probably freed by mrtg, and one reused for a new
> email.
>
If you've got files being deleted in the middle of the backup,  then it is 
extremely difficult for rsync (or any tool) to get the hard link detection 
correct.  You've got a few choices:

1) put everything on lvm and backup snapshots instead of the live filesystem.  
This has a number of benefits.

2) link everyfile into some temp directory before the backup starts.  This 
will prevent that particular inode number from being reused during the 
backup, but won't help if new files are added during the rsync (since those 
new files could also be deleted).

for each file in backup list
    ln file tmpdir/counter
    counter++
rsync
rm -rf  tmpdir

-chris