In Oracle 10g RAC and 11gR1 RAC, Oracle clusterware and ASM are installed
in the different Oracle homes, and the Clusterware has to be up before ASM
instance can be started because ASM instance uses the clusterware to access
the shared storage.
Oracle 11g R2 introduced the grid infrastructure home which combines Oracle
clusterware and ASM.
The OCR and voting disk of 11g R2 clusterware can be stored in ASM.
So it seems that ASM needs the clusterware up first to access the shared
storage and the clusterware needs ASM up first before it can access its
key data structure: OCR and voting disk.
So really clusterware and ASM, which one needs to be up first, and which
one has to wait for other? This seemed to be the chicken or the ego problem.
Oracle’s solution to this problem is to combines the clusterware and ASM
into a single Grid Infrastructure home and comes up a procedure with a
complex start up sequence which mixes the different components of clusterware
and ASM instance in order.
clusterware startup command $GI_HOME/bin/crsctl start crs follows this
sequence to bring both clusterware and ASM online
From this sequence of the log message and timestamp, we get some understanding
about the sequence of clusterware and ASM instance:
1) CSSD and CTSSD are up before ASM
2) Voting disks used by CSSD are discovered by reading the header of
the disks, not through ASM
3) Startup of CRS service has to wait until ASM instance is up and the
diskgroup for OCR and voting disk is mounted.
4) EVEMD and ACFS are up after the ASM starts.