The oracleasm scans /proc/partitions and expects devices to be available in /dev. If the device doesn't exist in /dev it will fail to open the device. RHEL/OEL5 does not create dm-xx devices in /dev by default.
Please comment out the following line in file /etc/udev/rules.d/50-udev.rules
#KERNEL=="dm-[0-9]*", ACTION=="add", OPTIONS+="ignore_device"
reboot and the problem should be gone.
domingo, 12 de dezembro de 2010