The outline of the steps involved are :
       a)  Backup all the ASM client database files stored on the diskgroups.
       b)  Dropping all the diskgroups.
       c)  Removing ASM resource from CRS (* RAC specific)
       d)  Removing ASM disk signature (In case of asmlib)
       e)  Remove the ASM pfile/spfile.
       f)  Removing ASM entry in the file oratab
       g)  Wipe out the disks header using dd

 

Following are the steps to be followed:
       1)  Log into the ASM instance and do 'select * from v$asm_client;'
       2)  For each instance listed above, stop the respective databases.
       3)  Backup all the datafiles, logfiles, controlfiles, archive logs, etc. that are currently using ASM storage, to tape or to filesystem (using RMAN). This needs to be done for every database (ASM client) using ASM.

       ** NOTE: Please make sure you have the data secure before continuing to the next step.

       4)  Find all the diskgroups: 'select * from v$asm_diskgroup'
       5)  For each diskgroup listed above:
              ' drop diskgroup <name> including contents'
       6)  Shutdown all(RAC nodes) ASM instances.

       7)  On RAC install verify that all asm instances are stopped
              $ORA_CRS_HOME/bin/crst_stat |more <- look for ASM resources and make sure the target=offline

       8)  For single instance install run the following script:
              $ORACLE_HOME/bin/localconfig  delete

              * This cleans up the CSSD configuration.

       9)  Invoke OUI, and now de-install the ASM Oracle home.

       10)  For RAC install, remove the asm related resource.
              srvctl remove asm -n <nodename> <- Peform for all nodes of a RAC cluster
              crs_stat |more <- make sure no asm resources existshttp://www.cndba.cn/Dave/article/846

       11)  If using asmlib (on Linux only), then
              a. oracleasm listdisks
              b. oracleasm deletedisks (do this for every disk listed above)
              c. oracleasm listdisks (to verify they have been deleted)
              d. on other RAC nodes: oracleasm listdisks (to verify they have been deleted too)
              e. On all nodes(RAC) :

       As root run:
              # /etc/init.d/oracleasm stop
              # /etc/init.d/oracleasm disable

       12)  delete the ASM pfile or spfilehttp://www.cndba.cn/Dave/article/846

       13)  in the file oratab, remove the line relative to the ASM instance

       14)  clean out the disks headers using the dd command:

              for example: dd if=/dev/zero of=/dev/<asm_disk_name> bs=1024k count=50

       15)  Finally clean out the possible remaining socket files as explained in the following note:

Listener Fails To Start With IPC Permission Errors (TNS-12546 TNS-12555 TNS-00516 TNS-00525) (Doc ID 434062.1)

 

 

 http://www.cndba.cn/Dave/article/846

 

From Oraclehttp://www.cndba.cn/Dave/article/846

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