In Red Hat Enterprise Linux 5, device-mapper-multipath is installed by default. This is a change from Red Hat Enterprise Linux 4. If a third party multipathing solution is in use, device-mapper-multipath should be disabled to avoid any conflict between multiple multipathing technologies. To disable device-mapper-multipath, turn it off with the following command:

# chkconfig multipathd off

In addition, make sure the /etc/sysconfig/mkinitrd/multipath file has the following line:
MULTIPATH=NO

By default, /etc/multipath.conf has all devices blacklisted. If this default configuration has been changed, the change should be reverted. If the devices are not blacklisted, then running the multipath command could cause a conflict with other multipathing software. The /etc/multipath.conf file should contain the following:

# Blacklist all devices by default. Remove this to enable multipathing
# on the default devices.
blacklist {
devnode "*"
}

These steps will ensure that device-mapper-multipath does not conflict with any other multipathing solution in use.