ASM and Clusterware: Which One is Started First?

If you have used Oracle RAC 10g and 11gR1, you might remember that the Oracle Clusterware stack has to be up before the ASM instance starts on the node. Because 11gR2, OCR, and VD also can be stored in ASM, the milliondollar question in everyone’s mind is, “Which one is started first?” This section will answer that interesting question.

The Clusterware startup sequence that we just discussed gives the solution: ASM is a part of the CRS of the Clusterware and it is started at Level 3 after the high availability stack is started and before CRSD is started.

Then, the question is, “How does the Clusterware get the stored cluster configuration and the clusterware membership information, which are normally stored in OCR and VD, respectively, without starting an ASM instance?” The answer is that during the startup of the high availability stack, the Oracle Clusterware gets the clusterware configuration from OLR and the GPnP profile instead of from OCR. Because these two components are stored in the $GRID_HOME in the local disk, the ASM instance and ASM diskgroup are not needed for the startup of the high availability stack. Oracle Clusterware also doesn’t rely on an ASM instance to access the VD.