Database Backup Fidelity: Why Crash-Consistent Is Not a Database Backup

The article distinguishes crash-consistent from app-consistent database backups. Crash-consistent snapshots capture disk state mid-transaction without database engine coordination, relying on WAL replay and log rollback at restore time—which can fail. App-consistent backups coordinate with the database engine to flush buffers and quiesce writes before snapshotting, producing a cleanly mountable backup. Most environments default to crash-consistent backups due to inherited VM snapshot tooling, uniform backup policies, and deferred integration work.