Cloud Backup and Disaster Recovery: Google Cloud, AWS, Azure

RPO is the acceptable duration of data loss after an incident. A backup schedule alone does not prove it: failed jobs or delayed replication to another site can enlarge the window. Compare the incident time with the latest usable, consistent recovery point. If an incident occurs at 14:00 and the verified copy is from 13:20, the observed loss window is 40 minutes. Set targets per application; a file archive and a database receiving continuous orders may have different requirements.

RTO specifies how soon a service must become usable after an incident. Downloading a backup or booting a VM accounts for only part of that duration. Record detection, approval, infrastructure preparation, data transfer, application startup and business validation separately. Define exactly what starts and stops the test clock. The same technical restore duration can produce different business interruptions when dependencies or access approvals introduce additional waiting.

Immutable retention restricts modification or deletion for a defined period. An application promise, storage-enforced protection and physical isolation are different controls. Review lock duration, clock handling, administrative privileges and deletion paths together. Whether data is automatically deleted after expiry depends on the product policy. On a controlled test copy, attempt deletion using ordinary and privileged accounts, then verify recovery from the protected copy. Protection against deletion does not replace a readability or restore test.

Replication transfers data or state changes to another copy. Synchronous transfer can introduce latency and connectivity dependence; asynchronous transfer can lag behind. A current replica is not necessarily protected from incorrect changes: deletion and corruption can propagate too. Compare lag with the application’s last committed operation, not merely connection status. Define which copy receives write authority after the source is lost and how the old node is reconciled when it returns. Report replication lag and the actual recoverable point separately.

Services commonly depend on identity, DNS, time, networking, databases and licensing. Record a dependency graph describing conditions for operation, not merely an equipment list. Recovery order follows that graph; circular dependencies may require emergency access paths. Distinguish restored infrastructure from resumed business activity. Assign an owner, validation method and alternative access path to each dependency. Test assumptions by deliberately making one component unavailable in a controlled end-to-end exercise.

A copy that boots does not prove application-data consistency. Operating-system caches, database logs and write ordering across disks or services affect the result. A crash-consistent copy resembles recovery after an unexpected shutdown; an application-consistent copy follows supported application preparation and write coordination. Validate transaction integrity, relationships between records and application behaviour after recovery, rather than only counting files. Confirm backup integration, application version and reported errors before assuming that consistency was achieved.