First, we check that the raw device has been added according to the specification given in the ASM parameter file. For that we check what is the value of ASM instance parameter ASM_DISKSTRING by doing following:
$ export ORACLE_SID=+ASM
$ sqlplus /nolog
sqlplus> conn / as sysdba
sqlplus> show parameter DISK
The above command will show the value of parameter ASM_DISKSTRING. e.g. /dev/rdsk/emcpower*
/dev/rdsk/emcpower* means that the raw devices which are eligible for ASM discovery should be in format /dev/rdsk/emcpower*. For example if a new raw device emcpower42g is added, then it would be eligible.
Now we will add this raw device as ASM disk in an existing ASM diskgroup.
We can check which ASM diskgroups are available from v$asm_diskgroup dynamic view.
alter diskgroup data add disk '/dev/rdsk/emcpower42g';
Now we can check the name and path of newly added ASM disk from v$ASM_DISK view.
select name, path from v$asm_disk;