What is it? Oracle Real Application Clusters, running one database across many servers.
Who is it for? Enterprises needing highly available, scalable database systems.
What does it cost? A licensed option on top of Oracle Database Enterprise Edition.
Where does it run? Clustered Linux, Unix and Windows servers with shared storage.
Oracle Real Application Clusters, or RAC, lets a single Oracle Database run simultaneously across multiple servers that all access the same shared storage. Instead of one machine being a single point of failure, several nodes cooperate as one logical database. If a node goes down, the surviving nodes keep serving transactions, and applications reconnect with minimal disruption — the foundation of continuous availability for mission-critical systems.
RAC delivers both resilience and scale. Workload is spread across nodes through services and load balancing, so you can add servers to handle more users rather than replacing a single big box. Oracle's Grid Infrastructure, Clusterware and Automatic Storage Management coordinate the cluster, manage the shared disks, and use Cache Fusion to move data blocks between nodes over a private interconnect, keeping every instance consistent.
RAC is an enterprise-grade capability compared against Microsoft SQL Server Always On, IBM Db2 pureScale, and PostgreSQL clustering solutions, and it is often paired with Data Guard for disaster recovery. Database architects search "oracle rac architecture", "cache fusion", "grid infrastructure install", "rac vs data guard" and "asm shared storage" when designing systems where downtime is simply not an option. Its complexity demands skilled DBAs but pays off in uptime.
| Function | Role in workflow |
|---|---|
| Multi-Node Database | Run one database across several servers |
| High Availability | Survive node failure without losing service |
| Cache Fusion | Share data blocks across nodes coherently |
| Load Balancing | Distribute connections and workload evenly |
| Grid Infrastructure | Manage cluster resources and startup |
| ASM Storage | Pool and manage shared database disks |
| Services & Failover | Route apps and reconnect on outages |
| Online Scaling | Add nodes to grow capacity live |
Together these components turn many servers into one resilient, scalable database.
Because RAC is an enterprise database technology, planning comes before anything else: provision at least two cluster nodes with a private interconnect and shared storage, then use the download button above to obtain the Grid Infrastructure and Database software. Confirm your operating system, network and storage meet Oracle's prerequisites before you begin.
Install Oracle Grid Infrastructure first to configure Clusterware and ASM across the nodes, then install the database software and create a clustered database with the Database Configuration Assistant. Define services to route application workloads, test node failover by shutting an instance down, and validate that clients reconnect automatically. Document the topology so the operations team can maintain and patch the cluster safely.
In production, RAC quietly keeps the database online while DBAs monitor node health, interconnect traffic and service placement. Routine tasks include patching one node at a time in a rolling fashion, rebalancing ASM storage as disks are added, and tuning services so busy workloads land on the right instances. When hardware fails, the cluster absorbs the loss and administrators replace the node without taking the application offline.
Scenario A A bank runs its core transaction database across nodes to guarantee 24/7 uptime.
Scenario B A DBA patches one cluster node at a time with no application downtime.
Scenario C A retailer adds a node before peak season to absorb higher traffic.
Scenario D A failed server is replaced while the surviving nodes keep serving queries.
| Item | Minimum | Recommended |
|---|---|---|
| OS | Oracle Linux, RHEL, or supported Unix/Windows | Certified Oracle Linux release |
| Nodes | 2 clustered servers | 3 or more nodes for capacity |
| CPU | Multi-core 64-bit per node | High-core-count server-grade CPUs |
| RAM | 8 GB per node | 32 GB or more per node |
| Storage | Shared storage (SAN/NAS) for ASM | Redundant shared storage with fast I/O |
| Network | Public plus private interconnect | Redundant high-speed interconnect |
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