4.4.3. Testing and Backups
š” First Principle: Untested backup and recovery plans are wishes, not plans. Regular testing validates that recovery procedures actually work under realistic conditions. Backup strategies must balance recovery speed, data completeness, and storage cost.
Testing types:
- Tabletop exercises ā stakeholders walk through a scenario verbally, discussing their responses. Lowest cost and disruption; tests decision-making, not technical capability.
- Failover testing ā actually switching to backup systems to verify they work. Tests technical readiness; risks production disruption.
- Simulation ā realistic scenario testing without affecting production. Tests both technical and procedural capabilities.
- Parallel processing ā running backup systems alongside production to verify they produce identical results before cutting over.
Backup types:
| Backup Type | What It Backs Up | Speed | Restore Time | Storage |
|---|---|---|---|---|
| Full | Everything | Slowest | Fastest | Most |
| Incremental | Changes since last backup (any type) | Fastest | Slowest (needs all incrementals) | Least |
| Differential | Changes since last full | Medium | Medium (needs full + latest diff) | Medium |
| Snapshot | Point-in-time system state | Fast | Fast | Varies |
Backup considerations: onsite backups for fast recovery, offsite backups for disaster recovery, encryption for backup data in transit and at rest, regular restore testing to verify backup integrity.
Replication ā real-time copying of data to a secondary location. Provides near-zero RPO but requires sufficient bandwidth and introduces complexity.
Journaling ā recording all changes to data in a transaction log, enabling point-in-time recovery by replaying or rolling back transactions.
ā ļø Exam Trap: Incremental backups are fastest to create but slowest to restore (you need the full backup plus every incremental since). Differential backups are a middle ground (you need only the full plus the latest differential). Know the trade-offs for each.
