Ok, so I  tried with -v -v and  -v -v -v, but this does  not give more
clue, only much more useless log data.
I still have the problem that with:
    rsync -v -auxHS --delete --force / /backup/
I get the following log:
    building file list ... done
    deleting var/cache/man/cat1/gcc.1.gz
    deleting var/cache/man/cat1/gawk.1.gz
    deleting var/account/pacct-20010930.gz
    deleting tmp/bounce/b1.mail
    deleting tmp/.#l.html
    deleting tmp/#l.html#
    dev/
    etc/
    etc/cups/certs/
    etc/cups/certs/0
    etc/ntp.drift
    [...]
    var/spool/postfix/incoming/F/1/
    var/spool/postfix/incoming/F/2/
    var/spool/postfix/incoming/F/3/
    var/spool/postfix/maildrop/
    var/tmp/
and then nothing more happens, it's blocked there.    
ps  shows that  the three  rsync  processes are  syspended waiting  on
do_sel (do_select).  A dead-lock I would say.
[root@thalassa root]# ps axflww | egrep rsync\|RSS\|backup
  F   UID   PID  PPID PRI  NI   VSZ  RSS WCHAN  STAT TTY        TIME COMMAND
000     0 19243 22982   9   0  2448  136 wait4  S    pts/2      0:00            
\_ /bin/bash /local/sbin/do-backup
004     0 19458 19243   9   0 65504 1152 do_sel S    pts/2      0:37            
|   \_ rsync -v -auxHS --delete --force / /backup/
006     0 19459 19458   9   0 172744 72228 do_sel S  pts/2      1:34            
|       \_ rsync -v -auxHS --delete --force / /backup/
006     0 19550 19459   9   0 172744 43360 do_sel S  pts/2      0:02            
|           \_ rsync -v -auxHS --delete --force / /backup/
000     0 19262 22982   9   0  1496  104 nanosl S    pts/2      0:00            
\_ tail -f /tmp/backup-19243.log
000     0 19779 22982  13   0  1568  536 pipe_w S    pts/2      0:00            
\_ egrep rsync|RSS|backup
If I kill the grandchild and the child, I get this additionnal log:
usr/lib/locale/kw_GB/LC_NAME => usr/lib/locale/kl_GL/LC_NAME
usr/lib/locale/nl_BE/LC_NAME => usr/lib/locale/kw_GB/LC_NAME
usr/lib/locale/nl_NL/LC_NAME => usr/lib/locale/nl_BE/LC_NAME
usr/lib/locale/nn_NO/LC_NAME => usr/lib/locale/nl_NL/LC_NAME
usr/lib/locale/no_NO/LC_NAME => usr/lib/locale/nn_NO/LC_NAME
[...]
usr/lib/locale/en_DK/LC_CTYPE => usr/lib/locale/en_CA/LC_CTYPE
usr/lib/locale/en_GB/LC_CTYPE => usr/lib/locale/en_DK/LC_CTYPE
usr/lib/locale/en_HK/LC_CTYPE => usr/lib/locale/en_GB/LC_CTYPE
usr/lib/locale/en_IE/LC_CTYPE => usr/lib/locale/en_HK/LC_CTYPE
unexpected EOF in read_timeout
Note the filesystems / and /backup:
Filesystem    Type    Size  Used Avail Use% Mounted on
/dev/hda2 reiserfs     12G   11G  787M  94% /
/dev/sda2 reiserfs     12G   11G  815M  94% /backup
-- 
__Pascal_Bourguignon__                   http://www.informatimago.com/
----------------------------------------------------------------------
 The name is Baud,...... James Baud.