PRIMECLUSTER Wizard for Oracle Configuration and Administration Guide 4.2 - Linux for Itanium -

2.4.2.2 Precaution for ASM operation

A disk group that is used for the ASM instance must not be mounted or unmounted manually. F the disk group is mounted, the following message might be output to the console when the ASM resource is activated, but no action needs to be taken.

ORA-15032: not all alterations performed
ORA-15017: diskgroup "diskgroup name" cannot be mounted
ORA-15030: diskgroup name "diskgroup name" is in use by another diskgroup