Installations of Debian Lenny during the BETA phase contain an erroneous initscript, which causes that the iscsid doesn't reconnect to the filer after a disconnection. Newly installed servers are not concerned. Please use this command to fix an existing BETA installation:

wget ftp://ftp.ovh.net/made-in-ovh/rps/open-iscsi -O /etc/init.d/open-iscsi && chmod +x /etc/init.d/open-iscsi && /etc/init.d/open-iscsi restart