RAC Startup Sequence

 In an Oracle RAC environment, multiple instances start up and mount one shared database. The startup is coordinated by Oracle Clusterware.

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🧩 RAC Startup Steps

1. Clusterware Startup (Infrastructure Layer)

• Before any database instance starts, Clusterware (CRS) must be running on all nodes.

• Clusterware includes:

  • Cluster Ready Services (CRS)

  • Oracle Cluster Synchronization Services (CSS)

  • Oracle High Availability Services (OHASD)

Commands:

crsctl start crs     # Start Clusterware stack on a node
crsctl check crs     # Verify status

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2. Automatic Startup of RAC Instances

• Once CRS is up, it will start:

  • Oracle ASM instances (if used)

  • Listener

  • Database instances (configured as resources in CRS)

Commands:

srvctl start asm -n <node_name>         # Start ASM on a specific node
srvctl start listener -n <node_name>    # Start listener on a node
srvctl start database -d <db_name>      # Start all RAC instances

• Alternatively, to start an instance manually (on one node):

sqlplus / as sysdba
STARTUP

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⚙ RAC Instance Startup Phases

Each RAC instance goes through these standard Oracle startup stages:

Stage	What Happens
STARTUP NOMOUNT	Allocates SGA, starts background processes. Uses init.ora / spfile
STARTUP MOUNT	Reads control files from shared storage. Opens redo threads.
STARTUP OPEN	Opens datafiles and online redo logs, database available to users

• At MOUNT, the instance joins the cluster group using Global Enqueue Service (GES) and Global Cache Service (GCS).

• At OPEN, the database becomes fully accessible.

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🔁 Typical RAC Startup Flow

[Start Clusterware] 
      ↓
[Start ASM Instances] 
      ↓
[Start Listeners] 
      ↓
[Start RAC Instances (Node1, Node2,...)]
      ↓
[Each instance does: NOMOUNT → MOUNT → OPEN]
      ↓
[Clustered Database becomes available]

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📌 Useful RAC Startup/Shutdown Commands

Task	Command
Start whole RAC DB	srvctl start database -d <db_name>
Stop whole RAC DB	srvctl stop database -d <db_name>
Start one instance	srvctl start instance -d <db_name> -i <inst_name>
Stop one instance	srvctl stop instance -d <db_name> -i <inst_name>
Check database status	srvctl status database -d <db_name>