Disaster-Recovery

Overview Both patterns keep a system running when a node fails, but they differ in whether every node is doing useful work all the time. Active-Active runs multiple nodes concurrently serving live traffic, while Active-Passive keeps a standby node idle until the primary fails. The choice affects utilization, cost, data consistency, and how much downtime you accept during failover. Comparison Diagram Active-ActiveActive-PassiveCLBNode 1Node 2both nodes serve live trafficfailure of one: LB reroutes instantlyCActiveStandbyreplicationon failure: promote standbybrief failover delay Comparison Table Aspect Active-Active Active-Passive Topology All nodes are equal peers running the same workload One primary node plus one or more idle standby nodes Traffic routing Load balancer distributes requests across every node All requests go to the single active node Resource utilization Full capacity of every node used continuously Standby capacity sits reserved but unused until needed Failure detection Health checks pull the unhealthy node out of the LB pool Heartbeat or monitor detects primary is down Failover behavior Near-instant; surviving nodes absorb load with no promotion step Standby must be promoted to primary, causing a brief outage Data consistency Requires conflict resolution or coordination across writable nodes Single writer at a time keeps consistency simple Cost efficiency No idle capacity; you pay for what’s used Pay for standby capacity that mostly sits idle Operational complexity Higher: multi-master sync, conflict handling, split-brain risk Lower: simple primary/standby roles, single write path Key Differences Active-Active serves traffic from every node simultaneously; Active-Passive serves it from only one at a time Failover in Active-Active is near-instant since surviving nodes are already live, while Active-Passive needs a promotion step Active-Active fully utilizes hardware; Active-Passive leaves standby capacity idle as insurance Multi-writer setups need conflict resolution, whereas a single active writer avoids that complexity entirely When to Use Each Active-Active ...

Overview A snapshot captures a volume’s state using copy-on-write pointers that still depend on the original data, while a backup creates a fully independent copy stored elsewhere. The distinction matters because snapshots are fast and space-efficient for short-term rollback, but only backups protect against loss or corruption of the source system itself. Comparison Diagram Source Volumepointer (COW)full copySnapshotreferences source blocksSame volume, low overheadInvalid if source is lostBackupindependent full copySeparate storage, survives lossSlower, higher storage cost Comparison Table Aspect Snapshot Backup Primary purpose Quick rollback to a prior state Durable copy for disaster recovery and compliance Capture mechanism Copy-on-write or redirect-on-write pointers to existing blocks Full or incremental copy of data written to separate storage Storage location Same storage system or volume as the source Separate system, often offsite or on a different medium Dependency on source Invalidated if the source volume is deleted or corrupted Independent copy, survives loss of the source Creation speed and overhead Near-instant, minimal I/O impact Slower, with higher I/O, network, and storage cost Retention and lifecycle Short-lived, few kept because storage grows with changes Long-term retention on a scheduled rotation policy Recovery scope Instant rollback on the same system or volume Restore to a new or different system, file- or volume-level Failure resilience Vulnerable to the same hardware or storage failure as the source Resilient to source failure or a site-wide disaster Key Differences A snapshot stores pointers to existing blocks; a backup writes a full, separate copy of the data. Snapshots normally live on the same storage as the source; backups are placed on independent, often offsite media. Deleting the source volume can invalidate a snapshot, while a backup remains intact and restorable. Snapshots are created almost instantly with low overhead; backups take longer and consume more storage and bandwidth. Snapshots are typically kept briefly for rollback; backups follow a long-term retention policy for compliance. When to Use Each Snapshot ...