Oracle RAC ASM diskgroup rename

Rename ASM diskgroup 

First, check there should not be any running transactions going on the diskgroup you are going to rename.

Dismount the DISKGROUP to be renamed on all the nodes

Run renamedg check for checking, it will let you know if any other steps needed before actual rename of diskgroup like dismount of diskgroup on another node

renamedg dgname=<old_dgname> newdgname=<new_dgname> verbose=true check=true

Now run the renamedg for renaming the diskgroup

renamedg dgname=<old_dgname> newdgname=<new_dgname> verbose=true

Mount the newly named DISKGROUP

Oracle RAC Clusterware 11gR2 startup sequence with explained diagram

When a RAC node of Cluster starts or restarts, first daemon to be started is OHASD by server specific cluster initialization procss.

OHASD has access to OLR i.e Oracle Local Registry stored on local system, which is just copy of OCR i.e. Oracle Clusterware Registry.

OLR contains the information required to complete the OHASD initialization.

OHASD brings up GPNP and CSSD as CSSD has access to GPNP Profile which contains below data required to start ASM instance

i.   ASM Diskgroup discovery string
ii.  ASM spfile location
iii. ASM all diskgroup details with the one, which is containing Voting Files

RAC Clusterware Startup Sequence

Once Voting Files are located and accessed by CSSD, CSSD is able to complete its initialization and join the existing cluster.

OHASD starts ASM instance which then starts operating with CSSD.

Once ASM instance started with its diskgroup mounted, OCR available on ASM diskgroup will be accessible to CRSD.

Clusterware completes its initialization and brings up other remaining daemons / services

Briefing about the files involved in the Clusterware startup

a) OLR - Oracle Local Registry, as the name suggests it is stored locally and kind of registry for RAC, 
which contains information regarding the location of voting disk and the information related to ASM instance startup as discussed above

b) Voting Disk - Contains the hearbeat of complete Clusterware, meaning it manages information about node membership.
It prevents Split-Brain scenarios

c) OCR - Oracle Clusterware Registry is the file which manages Cluster Configuration information