Oracle ASM oracleasm createdisk "Device or resource busy"

http://blogs.oracle.com/simonthorpe/2009/06/configuring_oracle_asm_disks_i.html

I was then able to mark my disks for ASM use, except I had already mounted these disks as part of my testing from earlier.

[root@database modules]# oracleasm createdisk DATADISK1 /dev/sdc1
Unable to open device "/dev/sdc1": Device or resource busy

Duh, I quickly removed the references in /etc/fstab and unmounted the drives. This time I could run my command;

[root@database modules]# oracleasm createdisk DATADISK1 /dev/sdc1
Writing disk header: done
Instantiating disk: done
[root@database modules]# oracleasm createdisk DATADISK2 /dev/sdd1
Writing disk header: done
Instantiating disk: done