Mark Wagner's Oracle on Linux Site

# /etc/init.d/oracleasm createdisk VOL1 /dev/xvdb1
Marking disk "/dev/xvdb1" as an ASM disk: asmtool: Device "/dev/xvdb1" is not
a partition
                                                           [FAILED]

Workaround: Run the asmtool command with the -a force=yes parameter to ignore the partition check, for example

# asmtool -C -l /dev/oracleasm -n VOL1 -s /dev/xvdb1 -a force=yes
/etc/init.d/oracleasm scandisks

The oracleasm scandisks command fixes permissions once the disk is created.