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Difficulty: Very hardResilience, High Availability, and Redundancy

An enterprise organization is designing a high-availability infrastructure for a mission-critical financial application. The business requirements state that the system must maintain a Recovery Point Objective (RPO) of zero and support automated failover across geographically separated data centers. The lead architect proposes an active-passive dual-datacenter configuration utilizing asynchronous storage volume replication and dynamic DNS routing to switch client traffic upon primary site failure. Which of the following evaluations best explains why this proposed design fails to meet the organization's requirements?

  1. Asynchronous storage replication allows transactions to commit locally before remote confirmation, creating a window for data loss that violates an RPO of zero during an unannounced failure.Answer
  2. B
    Asynchronous replication achieves hardware fault tolerance for active operations, but it cannot replace cold-site tape backups required for complete redundancy.
  3. C
    Dynamic DNS traffic routing functions purely as a detective control, failing to provide the automated corrective control capability required for fault-tolerant architectures.
  4. D
    Asynchronous storage replication successfully guarantees zero data loss, but it violates the RPO threshold because RPO defines the maximum allowable duration of service downtime.

Answer

Asynchronous storage replication allows transactions to commit locally before remote confirmation, creating a window for data loss that violates an RPO of zero during an unannounced failure.
Synchronous storage replication requires data to be written and acknowledged at both primary and secondary sites before a transaction is marked complete. Asynchronous storage replication, while offering lower latency across geographic distances, allows the primary storage system to acknowledge writes before they are transmitted to the secondary site. Consequently, if the primary site fails unexpectedly, any data in transit or queued for replication is lost, directly violating the requirement of an RPO of zero.

Step-by-Step Solution

1
Analyze the core architectural requirement
The requirement specifies an RPO (Recovery Point Objective) of zero, meaning no data loss is permitted during a failover event.
RPO defines the maximum tolerable period during which data might be lost due to a major incident.
2
Evaluate the capabilities of asynchronous storage replication
Asynchronous replication writes data to the primary storage first and acknowledges the write to the application immediately, sending data to the remote replica asynchronously.
This introduces a latency buffer where un-replicated transactions pending transfer will be lost if the primary site goes offline.
3
Identify the correct high-availability control required
Synchronous storage replication must be used to guarantee RPO = 0, as it requires write confirmation from both sites before committing.
Only synchronous replication ensures that no uncommitted data exists solely on the failing primary node.

Key Concept

Synchronous vs. Asynchronous Replication and RPO Bounds in High Availability Architectures
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Topics

Resilience, High Availability, and Redundancy

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