AWS RDS vs Aurora: Which Managed Database Is Right for You?

Amazon RDS and Aurora are both managed relational database services, but they are architecturally distinct products with different cost models, availability characteristics, and performance profiles. Aurora is often described as “RDS but faster” — that framing misses the nuance that matters for production architecture decisions.

This comparison focuses on the technical and economic differences that affect real workloads, including Aurora’s I/O pricing model that surprises teams when their first monthly bill arrives.

Architecture Differences

The most important difference between RDS and Aurora is the storage layer.

Standard RDS uses Amazon EBS volumes attached to the database instance. Replication (for Multi-AZ deployments) is handled at the storage level using synchronous EBS mirroring to a standby instance in a second Availability Zone. The storage grows in fixed increments and is bound to the instance’s EBS configuration.

Aurora uses a purpose-built distributed storage system that is decoupled from the compute layer. Aurora storage automatically replicates data 6 ways across 3 Availability Zones — this happens at the storage level, not the instance level. Aurora storage auto-scales in 10 GB increments up to 128 TiB. The compute (instances) and storage are independently scalable.

Performance Comparison

Aurora’s distributed storage architecture provides concrete advantages for specific workload patterns:

• Read scaling: Aurora Replicas share the same underlying storage as the primary. Replication lag is typically under 100ms (often milliseconds). RDS read replicas replicate via binary log replication, which introduces higher lag under write load.
• Failover speed: Aurora fails over to a read replica in ~30 seconds because the replica is already attached to the same storage. RDS Multi-AZ failover involves remounting EBS to the standby, typically taking 30–120 seconds.
• Crash recovery: Aurora’s distributed storage architecture means the database does not need to replay a redo log after a crash. Recovery is near-instant.

For write-heavy single-instance workloads, RDS and Aurora perform similarly. The Aurora storage layer’s 6-way write amplification means more I/O operations per write — which is why the I/O cost model matters.

Cost Breakdown

This is where Aurora’s real cost differs from marketing comparisons.

Aurora Standard (per-I/O pricing):

• Instance: ~20% premium over equivalent RDS instance
• Storage: $0.10/GB-month
• I/O requests: $0.20 per million requests
• Backup storage: $0.021/GB-month (beyond free tier)

Aurora I/O-Optimized (no per-I/O charge):

• Instance: ~30-40% premium over equivalent RDS instance
• Storage: $0.225/GB-month
• I/O requests: Included (no charge)
• Backup storage: $0.021/GB-month

RDS Provisioned (PostgreSQL/MySQL, gp3 storage):

• Instance: Baseline pricing
• Storage: $0.115/GB-month (gp3)
• I/O requests: No per-I/O charge
• Backup storage: $0.095/GB-month (beyond free tier)

Estimated monthly cost — db.r6g.large, 100 GB storage, us-east-1:

At 500 million I/O operations per month, Aurora Standard is more expensive than both RDS and Aurora I/O-Optimized. At 1 billion+ I/O operations per month, Aurora I/O-Optimized starts to deliver savings versus Aurora Standard, and its higher instance cost may still be less than RDS Multi-AZ for highly available deployments.

High-Availability Features

Aurora Global Database is a differentiated feature with no direct RDS equivalent — it replicates data to up to 5 secondary regions with typical replication lag under 1 second, enabling near-zero RPO cross-region disaster recovery and read traffic distribution to geographically distributed users.

When RDS Is the Right Choice

RDS is the appropriate choice when the workload does not justify Aurora’s cost or complexity premium.

Choose RDS when:

• Your workload is development, testing, or early-stage production (Aurora’s minimum cost is higher)
• You need Oracle or SQL Server (Aurora does not support these engines)
• Traffic and I/O volumes are low — Aurora Standard’s per-I/O charges add cost without proportional benefit
• You want the simplest pricing model without I/O charges
• A single-AZ deployment is acceptable and Multi-AZ cost is not justified
• You need a specific engine version not yet available in Aurora (Aurora PostgreSQL versions lag slightly)

When Aurora Is the Right Choice

Choose Aurora when:

• High availability with fast failover is a requirement (the 30-second vs 2-minute failover difference matters)
• You need more than 5 read replicas for read scaling
• Cross-region replication with sub-second RPO is required (Global Database)
• I/O workloads are high enough to justify the storage architecture benefits
• You want storage to auto-scale without manual provisioning
• Aurora Serverless v2 is attractive for variable workload patterns

Migration Path from RDS to Aurora

Aurora is wire-compatible with MySQL and PostgreSQL, so most application migrations are straightforward. AWS provides two migration paths: a snapshot restore (takes your RDS snapshot and restores it into Aurora format) and AWS Database Migration Service for live migrations with minimal downtime. Plan for testing Aurora’s parameter group differences and I/O cost modeling before migrating production workloads.

Selecting the right managed database service requires modeling your actual I/O patterns and availability requirements. Our team helps AWS customers right-size their database infrastructure. Contact us to discuss which managed database configuration fits your workload and budget.