RAC Services Startup Sequence
When an Oracle RAC cluster is started, the components must come up in a specific dependency order:
🧩 Step-by-Step Startup Order
| Order | Component | Description | Command (if manual) |
|---|---|---|---|
| 1️⃣ | OHAS (Oracle High Availability Services) | Base daemon on each node. Brings up local agents and monitors. | crsctl start has |
| 2️⃣ | CSSD (Cluster Synchronization Services Daemon) | Handles node membership and cluster heartbeat. | Auto via OHAS |
| 3️⃣ | CRSD (Cluster Ready Services Daemon) | Manages cluster resources (like databases, services, VIPs). | Auto via OHAS |
| 4️⃣ | EVMD (Event Manager Daemon) | Manages cluster events and notifications. | Auto via OHAS |
| 5️⃣ | ASM Instances | Provides shared storage (if using ASM). Must start before any database instances. | srvctl start asm -n <node> |
| 6️⃣ | Listener(s) | Handles client connections. Needed before database instances start. | srvctl start listener -n <node> |
| 7️⃣ | Database Instances | Each RAC instance on each node. They mount and open the shared database. | srvctl start instance -d <db> -i <inst> or srvctl start database -d <db> |
| 8️⃣ | RAC Services (DB Services) | Logical services running on top of the database. Enable workload balancing, failover, etc. | srvctl start service -d <db> -s <service> |
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