thanks for you quick answer !
I will do a reboot on that machine cause I do not know what files are involved.
Yesterday I did the reboot, here the results:
linux starts in maintenance mode
reiserfsck --check reports exit-code 4
reiserfsck --rebuild-tree runs pass 0, 1 but does not finish pass 2
reboot and run rebuild again for three times with the same result: hang in pass 2
support for ReiserFS no longer available (www.namesys.com
format with Ext3, restore data from backup
I hope Raid5 will run better on Ext3, ...