Scaling out means distributing work across multiple server resources rather than relying only on a larger machine. SQL Server offers several technologies, each with different goals and consistency properties.
Availability versus read capacity
Failover clustering and availability groups can support recovery from failures; readable secondaries, replication, and separate reporting systems may help distribute reads. They are not interchangeable and are not substitutes for backups.
Common architectures
Log shipping copies and restores transaction-log backups on a schedule and is useful for certain disaster-recovery designs. Transactional replication distributes changes to subscribers. Always On availability groups offer a separate high-availability approach with optional readable secondary replicas in supported configurations.
Historical features
Database mirroring and shared scalable database concepts occur in older tutorials and are not a sensible default for a new deployment. Confirm support, deprecation, edition, and licence requirements before selecting an architecture.
Design checklist
Define RPO, RTO, read/write ratio, transaction consistency needs, failover handling, network latency, and operational responsibilities. Load-test an actual application rather than assuming that adding a node doubles throughput.
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