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While creating ASM diskgroup or adding new disk to a existing diskgroup, Disk should be visible in V$ASM_DISK.

ASM discovers and examines the contents of all of the disks that are in the paths that you designated with values in the ASM_DISKSTRING initialization parameter.

As per Oracle Docs, Disk discovery also occurs when you:

- Run the ALTER DISKGROUP…ADD DISK and ALTER DISKGROUP…RESIZE DISK commands

- Query the V$ASM_DISKGROUP and V$ASM_DISK views

Note: – You should try to use V$ASM_DISK_STAT to get faster results as access to this view does not lead to Disk Discovery.

While creating ASM Diskgroup, Disk Discovery is the most common issue. This is mostly due to Disk permission issue or incorrect setting for ASM_DISKSTRING parameter.

So as to check this , you can use KFOD utility provided by Oracle.

This can be found in $ASM_HOME/bin directory. Help can be seen using

 oracle@asm]/home/oracle> kfod help=y

<span style="font-size:small;"><span style="font-family:Times New Roman;">_asm_a/llow_only_raw_disks<span>              </span>KFOD allow only raw devices [_asm_allow_</span></span>

<span style="font-size:small;"><span style="font-family:Times New Roman;">only_raw_disks=TRUE/(FALSE)]</span></span>

<span style="font-size:small;"><span style="font-family:Times New Roman;">_asm_l/ibraries<span>         </span>ASM Libraries[_asm_libraries='lib1','lib2',...]</span></span>

<span style="font-size:small;"><span style="font-family:Times New Roman;">_asms/id<span>                </span>ASM Instance[_asmsid=sid]</span></span>

<span style="font-size:small;"><span style="font-family:Times New Roman;">a/sm_diskstring<span>         </span>ASM Diskstring [asm_diskstring='discoverystring', 'disco</span></span><span style="font-size:small;"><span style="font-family:Times New Roman;">verystring' ...]</span></span>

<span style="font-size:small;"><span style="font-family:Times New Roman;">d/isks<span>          </span>Disks to discover [disks=raw,asm,all]</span></span>

<span style="font-size:small;"><span style="font-family:Times New Roman;">g/roup<span>          </span>Group discover [group=controlfile]</span></span>

<span style="font-size:small;"><span style="font-family:Times New Roman;">n/ohdr<span>          </span>KFOD header suppression [nohdr=TRUE/(FALSE)]</span></span>

<span style="font-size:small;"><span style="font-family:Times New Roman;">o/p<span>             </span>KFOD options type [OP=DISKS/GROUPS/ALL]</span></span>

<span style="font-size:small;"><span style="font-family:Times New Roman;">p/file<span>          </span>ASM parameter file [pfile='parameterfile']</span></span>

<span style="font-size:small;"><span style="font-family:Times New Roman;">s/tatus<span>    </span><span>     </span>Include disk header status [status=TRUE/(FALSE)]</span></span>

<span style="font-size:small;"><span style="font-family:Times New Roman;">v/erbose<span>                </span>KFOD verbose errors [verbose=TRUE/(FALSE)]</span></span>

<span style="font-size:small;font-family:Times New Roman;">KFOD-01000: file not found</span>

To discover the disks , you need to use disks=all clause

[oracle@asm] /home/oracle&gt;kfod disks=all</span>
kfod disks=all
--------------------------------------------------------------------------------
 Disk          Size Path
==================================================================
   1:     345648 Mb /dev/sda7
--------------------------------------------------------------------------------
ORACLE_SID ORACLE_HOME
==================================================================
     +ASM2 /u01/app/oracle/product/asm10.2
     +ASM1 /u01/app/oracle/product/asm10.2
    

As seen from help menu, we can use raw and asm as option. One more important parameter which can be used is asm_diskstring to make sure that problem is not with initialization parameter.

[oracle@asm]/home/oracle>kfod asm_diskstring='/raw/*' disks=all
--------------------------------------------------------------------------------
ORACLE_SID ORACLE_HOME
====================================================================
     +ASM2 /u01/app/oracle/product/asm10.2
     +ASM1 /u01/app/oracle/product/asm10.2

By default asm_diskstring looks in all the directories.